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 $208.57   7.721%   $224.6737   $224.67   $224.65   $224.70  
  Purchase #2 $98.35   12.107%   $110.2572   $110.26   $110.25   $110.30  
  Purchase #3 $171.36   3.263%   $176.9515   $176.95   $176.95   $177.00  
  Purchase #4 $247.91   6.302%   $263.5333   $263.53   $263.55   $263.50  
  Purchase #5 $205.71   6.216%   $218.4969   $218.50   $218.50   $218.50  
  Purchase #6 $179.87   7.197%   $192.8152   $192.82   $192.80   $192.80  
  Purchase #7 $93.72   6.636%   $99.9393   $99.94   $99.95   $99.90  
  7 purchase totals = $1,205.49       $1,286.6671   $1,286.67   $1,286.65   $1,286.70