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 $87.97   11.688%   $98.2519   $98.25   $98.25   $98.30  
  Purchase #2 $234.46   4.813%   $245.7446   $245.74   $245.75   $245.70  
  Purchase #3 $92.77   12.304%   $104.1844   $104.18   $104.20   $104.20  
  Purchase #4 $45.70   12.312%   $51.3266   $51.33   $51.35   $51.30  
  Purchase #5 $29.51   13.672%   $33.5446   $33.54   $33.55   $33.50  
  Purchase #6 $224.71   7.687%   $241.9835   $241.98   $242.00   $242.00  
  Purchase #7 $235.76   3.516%   $244.0493   $244.05   $244.05   $244.00  
  7 purchase totals = $950.88       $1,019.0849   $1,019.07   $1,019.15   $1,019.00