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 $67.52   7.258%   $72.4206   $72.42   $72.40   $72.40  
  Purchase #2 $90.66   11.758%   $101.3198   $101.32   $101.30   $101.30  
  Purchase #3 $57.87   11.541%   $64.5488   $64.55   $64.55   $64.50  
  Purchase #4 $68.28   13.524%   $77.5142   $77.51   $77.50   $77.50  
  Purchase #5 $222.43   10.729%   $246.2945   $246.29   $246.30   $246.30  
  Purchase #6 $55.92   13.217%   $63.3109   $63.31   $63.30   $63.30  
  Purchase #7 $200.32   12.489%   $225.338   $225.34   $225.35   $225.30  
  7 purchase totals = $763.00       $850.7468   $850.74   $850.70   $850.60