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 $234.62   13.870%   $267.1618   $267.16   $267.15   $267.20  
  Purchase #2 $112.86   10.701%   $124.9371   $124.94   $124.95   $124.90  
  Purchase #3 $109.95   8.406%   $119.1924   $119.19   $119.20   $119.20  
  Purchase #4 $39.70   12.191%   $44.5398   $44.54   $44.55   $44.50  
  Purchase #5 $220.59   11.576%   $246.1255   $246.13   $246.15   $246.10  
  Purchase #6 $236.66   3.732%   $245.4922   $245.49   $245.50   $245.50  
  Purchase #7 $69.42   9.275%   $75.8587   $75.86   $75.85   $75.90  
  7 purchase totals = $1,023.80       $1,123.3075   $1,123.31   $1,123.35   $1,123.30