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 $96.65   11.170%   $107.4458   $107.45   $107.45   $107.40  
  Purchase #2 $195.67   10.505%   $216.2251   $216.23   $216.25   $216.20  
  Purchase #3 $40.38   7.212%   $43.2922   $43.29   $43.30   $43.30  
  Purchase #4 $157.60   4.112%   $164.0805   $164.08   $164.10   $164.10  
  Purchase #5 $57.65   9.633%   $63.2034   $63.20   $63.20   $63.20  
  Purchase #6 $10.83   6.289%   $11.5111   $11.51   $11.50   $11.50  
  Purchase #7 $159.85   5.341%   $168.3876   $168.39   $168.40   $168.40  
  7 purchase totals = $718.63       $774.1457   $774.15   $774.20   $774.10