Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $182.87   12.498%   $205.7251   $205.73   $205.75   $205.70  
  Purchase #2 $209.43   3.353%   $216.4522   $216.45   $216.45   $216.50  
  Purchase #3 $130.51   13.804%   $148.5256   $148.53   $148.55   $148.50  
  Purchase #4 $163.33   12.810%   $184.2526   $184.25   $184.25   $184.30  
  Purchase #5 $162.59   8.771%   $176.8508   $176.85   $176.85   $176.90  
  Purchase #6 $221.94   4.241%   $231.3525   $231.35   $231.35   $231.40  
  Purchase #7 $250.25   13.107%   $283.0503   $283.05   $283.05   $283.10  
  7 purchase totals = $1,320.92       $1,446.2091   $1,446.21   $1,446.25   $1,446.40