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 $58.31   12.486%   $65.5906   $65.59   $65.60   $65.60  
  Purchase #2 $170.69   10.576%   $188.7422   $188.74   $188.75   $188.70  
  Purchase #3 $203.35   3.212%   $209.8816   $209.88   $209.90   $209.90  
  Purchase #4 $179.64   11.595%   $200.4693   $200.47   $200.45   $200.50  
  Purchase #5 $37.68   4.113%   $39.2298   $39.23   $39.25   $39.20  
  Purchase #6 $101.58   13.499%   $115.2923   $115.29   $115.30   $115.30  
  Purchase #7 $5.59   11.828%   $6.2512   $6.25   $6.25   $6.30  
  7 purchase totals = $756.84       $825.4570   $825.45   $825.50   $825.50