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 $57.67   7.186%   $61.8142   $61.81   $61.80   $61.80  
  Purchase #2 $193.27   6.405%   $205.6489   $205.65   $205.65   $205.60  
  Purchase #3 $205.63   5.691%   $217.3324   $217.33   $217.35   $217.30  
  Purchase #4 $168.32   3.222%   $173.7433   $173.74   $173.75   $173.70  
  Purchase #5 $86.77   6.492%   $92.4031   $92.40   $92.40   $92.40  
  Purchase #6 $115.44   5.290%   $121.5468   $121.55   $121.55   $121.50  
  Purchase #7 $54.63   5.476%   $57.6215   $57.62   $57.60   $57.60  
  7 purchase totals = $881.73       $930.1102   $930.10   $930.10   $929.90