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 $218.25   8.365%   $236.5066   $236.51   $236.50   $236.50  
  Purchase #2 $244.69   10.479%   $270.3311   $270.33   $270.35   $270.30  
  Purchase #3 $15.56   5.207%   $16.3702   $16.37   $16.35   $16.40  
  Purchase #4 $35.29   3.117%   $36.39   $36.39   $36.40   $36.40  
  Purchase #5 $78.76   5.600%   $83.1706   $83.17   $83.15   $83.20  
  Purchase #6 $246.68   12.254%   $276.9082   $276.91   $276.90   $276.90  
  Purchase #7 $121.89   6.668%   $130.0176   $130.02   $130.00   $130.00  
  7 purchase totals = $961.12       $1,049.6943   $1,049.70   $1,049.65   $1,049.70