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 $114.88   8.528%   $124.677   $124.68   $124.70   $124.70  
  Purchase #2 $226.74   6.687%   $241.9021   $241.90   $241.90   $241.90  
  Purchase #3 $32.70   9.452%   $35.7908   $35.79   $35.80   $35.80  
  Purchase #4 $148.57   11.217%   $165.2351   $165.24   $165.25   $165.20  
  Purchase #5 $93.95   11.698%   $104.9403   $104.94   $104.95   $104.90  
  Purchase #6 $140.80   7.616%   $151.5233   $151.52   $151.50   $151.50  
  Purchase #7 $83.37   9.371%   $91.1826   $91.18   $91.20   $91.20  
  7 purchase totals = $841.01       $915.2512   $915.25   $915.30   $915.20