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 $61.85   13.735%   $70.3451   $70.35   $70.35   $70.30  
  Purchase #2 $194.53   9.781%   $213.557   $213.56   $213.55   $213.60  
  Purchase #3 $20.93   8.783%   $22.7683   $22.77   $22.75   $22.80  
  Purchase #4 $221.34   8.336%   $239.7909   $239.79   $239.80   $239.80  
  Purchase #5 $184.27   9.854%   $202.428   $202.43   $202.45   $202.40  
  Purchase #6 $240.95   12.660%   $271.4543   $271.45   $271.45   $271.50  
  Purchase #7 $91.83   10.601%   $101.5649   $101.56   $101.55   $101.60  
  7 purchase totals = $1,015.70       $1,121.9085   $1,121.91   $1,121.90   $1,122.00