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 $86.38   8.726%   $93.9175   $93.92   $93.90   $93.90  
  Purchase #2 $244.49   11.341%   $272.2176   $272.22   $272.20   $272.20  
  Purchase #3 $123.40   9.779%   $135.4673   $135.47   $135.45   $135.50  
  Purchase #4 $69.69   3.567%   $72.1758   $72.18   $72.20   $72.20  
  Purchase #5 $60.35   8.493%   $65.4755   $65.48   $65.50   $65.50  
  Purchase #6 $55.83   7.800%   $60.1847   $60.18   $60.20   $60.20  
  Purchase #7 $236.55   4.200%   $246.4851   $246.49   $246.50   $246.50  
  7 purchase totals = $876.69       $945.9235   $945.94   $945.95   $946.00