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 $73.59   13.599%   $83.5975   $83.60   $83.60   $83.60  
  Purchase #2 $241.87   8.729%   $262.9828   $262.98   $263.00   $263.00  
  Purchase #3 $59.37   13.517%   $67.395   $67.40   $67.40   $67.40  
  Purchase #4 $110.54   6.213%   $117.4079   $117.41   $117.40   $117.40  
  Purchase #5 $226.71   4.567%   $237.0638   $237.06   $237.05   $237.10  
  Purchase #6 $127.89   8.389%   $138.6187   $138.62   $138.60   $138.60  
  Purchase #7 $36.39   13.290%   $41.2262   $41.23   $41.25   $41.20  
  7 purchase totals = $876.36       $948.2919   $948.30   $948.30   $948.30