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 $191.55   12.382%   $215.2677   $215.27   $215.25   $215.30  
  Purchase #2 $59.85   3.599%   $62.004   $62.00   $62.00   $62.00  
  Purchase #3 $74.31   11.646%   $82.9641   $82.96   $82.95   $83.00  
  Purchase #4 $64.70   5.797%   $68.4507   $68.45   $68.45   $68.50  
  Purchase #5 $158.35   9.467%   $173.341   $173.34   $173.35   $173.30  
  Purchase #6 $193.73   8.707%   $210.5981   $210.60   $210.60   $210.60  
  Purchase #7 $224.79   3.601%   $232.8847   $232.88   $232.90   $232.90  
  7 purchase totals = $967.28       $1,045.5103   $1,045.50   $1,045.50   $1,045.60