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 $60.42   12.592%   $68.0281   $68.03   $68.05   $68.00  
  Purchase #2 $114.86   9.357%   $125.6075   $125.61   $125.60   $125.60  
  Purchase #3 $209.49   7.441%   $225.0782   $225.08   $225.10   $225.10  
  Purchase #4 $207.63   13.662%   $235.9964   $236.00   $236.00   $236.00  
  Purchase #5 $92.96   12.728%   $104.7919   $104.79   $104.80   $104.80  
  Purchase #6 $92.57   7.616%   $99.6201   $99.62   $99.60   $99.60  
  Purchase #7 $18.67   11.706%   $20.8555   $20.86   $20.85   $20.90  
  7 purchase totals = $796.60       $879.9777   $879.99   $880.00   $880.00