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 $120.32   4.531%   $125.7717   $125.77   $125.75   $125.80  
  Purchase #2 $182.98   9.827%   $200.9614   $200.96   $200.95   $201.00  
  Purchase #3 $25.99   3.731%   $26.9597   $26.96   $26.95   $27.00  
  Purchase #4 $55.78   4.865%   $58.4937   $58.49   $58.50   $58.50  
  Purchase #5 $132.67   11.816%   $148.3463   $148.35   $148.35   $148.30  
  Purchase #6 $56.50   6.344%   $60.0844   $60.08   $60.10   $60.10  
  Purchase #7 $55.49   6.109%   $58.8799   $58.88   $58.90   $58.90  
  7 purchase totals = $629.73       $679.4971   $679.49   $679.50   $679.60