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 $95.51   9.175%   $104.273   $104.27   $104.25   $104.30  
  Purchase #2 $92.97   8.189%   $100.5833   $100.58   $100.60   $100.60  
  Purchase #3 $61.47   12.803%   $69.34   $69.34   $69.35   $69.30  
  Purchase #4 $202.56   8.265%   $219.3016   $219.30   $219.30   $219.30  
  Purchase #5 $170.96   7.145%   $183.1751   $183.18   $183.20   $183.20  
  Purchase #6 $8.45   9.273%   $9.2336   $9.23   $9.25   $9.20  
  Purchase #7 $149.74   7.462%   $160.9136   $160.91   $160.90   $160.90  
  7 purchase totals = $781.66       $846.8202   $846.81   $846.85   $846.80