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 $247.53   11.293%   $275.4836   $275.48   $275.50   $275.50  
  Purchase #2 $223.81   10.712%   $247.7845   $247.78   $247.80   $247.80  
  Purchase #3 $58.79   6.254%   $62.4667   $62.47   $62.45   $62.50  
  Purchase #4 $239.98   12.307%   $269.5143   $269.51   $269.50   $269.50  
  Purchase #5 $12.91   5.360%   $13.602   $13.60   $13.60   $13.60  
  Purchase #6 $6.82   3.431%   $7.054   $7.05   $7.05   $7.10  
  Purchase #7 $66.34   3.468%   $68.6407   $68.64   $68.65   $68.60  
  7 purchase totals = $856.18       $944.5458   $944.53   $944.55   $944.60