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 $58.92   8.163%   $63.7296   $63.73   $63.75   $63.70  
  Purchase #2 $205.53   5.107%   $216.0264   $216.03   $216.05   $216.00  
  Purchase #3 $55.84   11.251%   $62.1226   $62.12   $62.10   $62.10  
  Purchase #4 $217.91   5.331%   $229.5268   $229.53   $229.55   $229.50  
  Purchase #5 $63.58   10.811%   $70.4536   $70.45   $70.45   $70.50  
  Purchase #6 $174.88   7.397%   $187.8159   $187.82   $187.80   $187.80  
  Purchase #7 $156.93   10.637%   $173.6226   $173.62   $173.60   $173.60  
  7 purchase totals = $933.59       $1,003.2975   $1,003.30   $1,003.30   $1,003.20