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 $212.96   9.102%   $232.3436   $232.34   $232.35   $232.30  
  Purchase #2 $91.75   11.782%   $102.56   $102.56   $102.55   $102.60  
  Purchase #3 $156.30   5.146%   $164.3432   $164.34   $164.35   $164.30  
  Purchase #4 $25.68   8.160%   $27.7755   $27.78   $27.80   $27.80  
  Purchase #5 $190.79   10.559%   $210.9355   $210.94   $210.95   $210.90  
  Purchase #6 $51.72   12.656%   $58.2657   $58.27   $58.25   $58.30  
  Purchase #7 $44.48   4.581%   $46.5176   $46.52   $46.50   $46.50  
  7 purchase totals = $773.68       $842.7411   $842.75   $842.75   $842.70