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 $200.96   9.113%   $219.2735   $219.27   $219.25   $219.30  
  Purchase #2 $241.42   10.436%   $266.6146   $266.61   $266.60   $266.60  
  Purchase #3 $27.31   9.549%   $29.9178   $29.92   $29.90   $29.90  
  Purchase #4 $107.87   10.243%   $118.9191   $118.92   $118.90   $118.90  
  Purchase #5 $83.26   11.258%   $92.6334   $92.63   $92.65   $92.60  
  Purchase #6 $154.91   6.114%   $164.3812   $164.38   $164.40   $164.40  
  Purchase #7 $110.78   8.624%   $120.3337   $120.33   $120.35   $120.30  
  7 purchase totals = $926.51       $1,012.0733   $1,012.06   $1,012.05   $1,012.00