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 $88.78   8.693%   $96.4976   $96.50   $96.50   $96.50  
  Purchase #2 $188.87   11.730%   $211.0245   $211.02   $211.00   $211.00  
  Purchase #3 $122.62   7.127%   $131.3591   $131.36   $131.35   $131.40  
  Purchase #4 $40.31   9.131%   $43.9907   $43.99   $44.00   $44.00  
  Purchase #5 $149.28   3.621%   $154.6854   $154.69   $154.70   $154.70  
  Purchase #6 $46.83   9.840%   $51.4381   $51.44   $51.45   $51.40  
  Purchase #7 $118.75   11.824%   $132.791   $132.79   $132.80   $132.80  
  7 purchase totals = $755.44       $821.7864   $821.79   $821.80   $821.80