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 $238.32   8.383%   $258.2984   $258.30   $258.30   $258.30  
  Purchase #2 $209.97   12.721%   $236.6803   $236.68   $236.70   $236.70  
  Purchase #3 $113.84   13.468%   $129.172   $129.17   $129.15   $129.20  
  Purchase #4 $187.77   13.366%   $212.8673   $212.87   $212.85   $212.90  
  Purchase #5 $69.87   7.306%   $74.9747   $74.97   $74.95   $75.00  
  Purchase #6 $163.99   10.811%   $181.719   $181.72   $181.70   $181.70  
  Purchase #7 $62.50   5.581%   $65.9881   $65.99   $66.00   $66.00  
  7 purchase totals = $1,046.26       $1,159.6998   $1,159.70   $1,159.65   $1,159.80