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 $243.71   5.814%   $257.8793   $257.88   $257.90   $257.90  
  Purchase #2 $29.66   8.307%   $32.1239   $32.12   $32.10   $32.10  
  Purchase #3 $62.28   8.604%   $67.6386   $67.64   $67.65   $67.60  
  Purchase #4 $45.79   5.235%   $48.1871   $48.19   $48.20   $48.20  
  Purchase #5 $186.65   4.264%   $194.6088   $194.61   $194.60   $194.60  
  Purchase #6 $237.95   6.867%   $254.29   $254.29   $254.30   $254.30  
  Purchase #7 $173.61   5.138%   $182.5301   $182.53   $182.55   $182.50  
  7 purchase totals = $979.65       $1,037.2578   $1,037.26   $1,037.30   $1,037.20