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 $58.53   6.504%   $62.3368   $62.34   $62.35   $62.30  
  Purchase #2 $227.84   7.567%   $245.0807   $245.08   $245.10   $245.10  
  Purchase #3 $99.88   8.410%   $108.2799   $108.28   $108.30   $108.30  
  Purchase #4 $52.76   10.480%   $58.2892   $58.29   $58.30   $58.30  
  Purchase #5 $83.80   5.116%   $88.0872   $88.09   $88.10   $88.10  
  Purchase #6 $159.67   4.406%   $166.7051   $166.71   $166.70   $166.70  
  Purchase #7 $196.82   3.661%   $204.0256   $204.03   $204.05   $204.00  
  7 purchase totals = $879.30       $932.8045   $932.82   $932.90   $932.80