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 $50.90   13.764%   $57.9059   $57.91   $57.90   $57.90  
  Purchase #2 $197.34   4.818%   $206.8478   $206.85   $206.85   $206.80  
  Purchase #3 $118.27   7.752%   $127.4383   $127.44   $127.45   $127.40  
  Purchase #4 $104.97   10.661%   $116.1609   $116.16   $116.15   $116.20  
  Purchase #5 $54.36   10.671%   $60.1608   $60.16   $60.15   $60.20  
  Purchase #6 $26.54   9.631%   $29.0961   $29.10   $29.10   $29.10  
  Purchase #7 $105.84   9.754%   $116.1636   $116.16   $116.15   $116.20  
  7 purchase totals = $658.22       $713.7734   $713.78   $713.75   $713.80