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 $141.54   8.593%   $153.7025   $153.70   $153.70   $153.70  
  Purchase #2 $54.95   13.620%   $62.4342   $62.43   $62.45   $62.40  
  Purchase #3 $246.75   11.744%   $275.7283   $275.73   $275.75   $275.70  
  Purchase #4 $28.94   10.504%   $31.9799   $31.98   $32.00   $32.00  
  Purchase #5 $98.49   4.341%   $102.7655   $102.77   $102.75   $102.80  
  Purchase #6 $45.82   9.408%   $50.1307   $50.13   $50.15   $50.10  
  Purchase #7 $118.51   6.782%   $126.5473   $126.55   $126.55   $126.50  
  7 purchase totals = $735.00       $803.2884   $803.29   $803.35   $803.20