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 $52.92   6.427%   $56.3212   $56.32   $56.30   $56.30  
  Purchase #2 $101.79   11.243%   $113.2342   $113.23   $113.25   $113.20  
  Purchase #3 $237.54   3.103%   $244.9109   $244.91   $244.90   $244.90  
  Purchase #4 $54.51   13.201%   $61.7059   $61.71   $61.70   $61.70  
  Purchase #5 $190.68   12.650%   $214.801   $214.80   $214.80   $214.80  
  Purchase #6 $185.98   12.552%   $209.3242   $209.32   $209.30   $209.30  
  Purchase #7 $72.70   5.349%   $76.5887   $76.59   $76.60   $76.60  
  7 purchase totals = $896.12       $976.8861   $976.88   $976.85   $976.80