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 $51.44   13.200%   $58.2301   $58.23   $58.25   $58.20  
  Purchase #2 $212.36   5.735%   $224.5388   $224.54   $224.55   $224.50  
  Purchase #3 $153.29   4.773%   $160.6065   $160.61   $160.60   $160.60  
  Purchase #4 $60.71   5.424%   $64.0029   $64.00   $64.00   $64.00  
  Purchase #5 $59.50   11.352%   $66.2544   $66.25   $66.25   $66.30  
  Purchase #6 $231.99   3.750%   $240.6896   $240.69   $240.70   $240.70  
  Purchase #7 $106.57   10.317%   $117.5648   $117.56   $117.55   $117.60  
  7 purchase totals = $875.86       $931.8871   $931.88   $931.90   $931.90