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 $235.88   10.460%   $260.553   $260.55   $260.55   $260.60  
  Purchase #2 $136.26   4.692%   $142.6533   $142.65   $142.65   $142.70  
  Purchase #3 $228.47   7.870%   $246.4506   $246.45   $246.45   $246.50  
  Purchase #4 $151.89   3.327%   $156.9434   $156.94   $156.95   $156.90  
  Purchase #5 $61.33   13.753%   $69.7647   $69.76   $69.75   $69.80  
  Purchase #6 $33.70   8.394%   $36.5288   $36.53   $36.55   $36.50  
  Purchase #7 $202.63   7.266%   $217.3531   $217.35   $217.35   $217.40  
  7 purchase totals = $1,050.16       $1,130.2469   $1,130.23   $1,130.25   $1,130.40