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 $125.27   13.549%   $142.2428   $142.24   $142.25   $142.20  
  Purchase #2 $121.62   8.354%   $131.7801   $131.78   $131.80   $131.80  
  Purchase #3 $202.40   3.370%   $209.2209   $209.22   $209.20   $209.20  
  Purchase #4 $238.75   13.532%   $271.0577   $271.06   $271.05   $271.10  
  Purchase #5 $16.94   5.592%   $17.8873   $17.89   $17.90   $17.90  
  Purchase #6 $128.58   5.754%   $135.9785   $135.98   $136.00   $136.00  
  Purchase #7 $38.62   8.260%   $41.81   $41.81   $41.80   $41.80  
  7 purchase totals = $872.18       $949.9773   $949.98   $950.00   $950.00