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 $70.93   6.132%   $75.2794   $75.28   $75.30   $75.30  
  Purchase #2 $177.88   4.359%   $185.6338   $185.63   $185.65   $185.60  
  Purchase #3 $113.78   9.460%   $124.5436   $124.54   $124.55   $124.50  
  Purchase #4 $116.65   13.272%   $132.1318   $132.13   $132.15   $132.10  
  Purchase #5 $178.69   4.277%   $186.3326   $186.33   $186.35   $186.30  
  Purchase #6 $201.28   12.758%   $226.9593   $226.96   $226.95   $227.00  
  Purchase #7 $19.88   9.860%   $21.8402   $21.84   $21.85   $21.80  
  7 purchase totals = $879.09       $952.7207   $952.71   $952.80   $952.60