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 $69.74   13.696%   $79.2916   $79.29   $79.30   $79.30  
  Purchase #2 $107.93   4.613%   $112.9088   $112.91   $112.90   $112.90  
  Purchase #3 $64.90   9.182%   $70.8591   $70.86   $70.85   $70.90  
  Purchase #4 $118.32   4.485%   $123.6267   $123.63   $123.65   $123.60  
  Purchase #5 $226.31   6.698%   $241.4682   $241.47   $241.45   $241.50  
  Purchase #6 $189.38   6.202%   $201.1253   $201.13   $201.15   $201.10  
  Purchase #7 $116.47   6.422%   $123.9497   $123.95   $123.95   $123.90  
  7 purchase totals = $893.05       $953.2294   $953.24   $953.25   $953.20