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 $104.75   10.809%   $116.0724   $116.07   $116.05   $116.10  
  Purchase #2 $167.46   10.634%   $185.2677   $185.27   $185.25   $185.30  
  Purchase #3 $243.73   4.152%   $253.8497   $253.85   $253.85   $253.80  
  Purchase #4 $86.70   9.847%   $95.2373   $95.24   $95.25   $95.20  
  Purchase #5 $207.30   10.740%   $229.564   $229.56   $229.55   $229.60  
  Purchase #6 $197.26   7.713%   $212.4747   $212.47   $212.45   $212.50  
  Purchase #7 $149.56   5.593%   $157.9249   $157.92   $157.90   $157.90  
  7 purchase totals = $1,156.76       $1,250.3907   $1,250.38   $1,250.30   $1,250.40