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 $102.26   3.634%   $105.9761   $105.98   $106.00   $106.00  
  Purchase #2 $148.74   4.177%   $154.9529   $154.95   $154.95   $155.00  
  Purchase #3 $75.80   10.777%   $83.969   $83.97   $83.95   $84.00  
  Purchase #4 $216.73   10.478%   $239.439   $239.44   $239.45   $239.40  
  Purchase #5 $241.65   7.642%   $260.1169   $260.12   $260.10   $260.10  
  Purchase #6 $32.38   11.788%   $36.197   $36.20   $36.20   $36.20  
  Purchase #7 $77.36   3.297%   $79.9106   $79.91   $79.90   $79.90  
  7 purchase totals = $894.92       $960.5615   $960.57   $960.55   $960.60