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 $46.95   12.126%   $52.6432   $52.64   $52.65   $52.60  
  Purchase #2 $213.51   10.282%   $235.4631   $235.46   $235.45   $235.50  
  Purchase #3 $119.73   13.223%   $135.5619   $135.56   $135.55   $135.60  
  Purchase #4 $247.96   12.828%   $279.7683   $279.77   $279.75   $279.80  
  Purchase #5 $11.39   7.114%   $12.2003   $12.20   $12.20   $12.20  
  Purchase #6 $107.43   7.865%   $115.8794   $115.88   $115.90   $115.90  
  Purchase #7 $6.30   8.349%   $6.826   $6.83   $6.85   $6.80  
  7 purchase totals = $753.27       $838.3422   $838.34   $838.35   $838.40