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 $92.93   5.711%   $98.2372   $98.24   $98.25   $98.20  
  Purchase #2 $214.95   7.260%   $230.5554   $230.56   $230.55   $230.60  
  Purchase #3 $239.58   4.741%   $250.9385   $250.94   $250.95   $250.90  
  Purchase #4 $90.87   12.454%   $102.1869   $102.19   $102.20   $102.20  
  Purchase #5 $195.37   5.419%   $205.9571   $205.96   $205.95   $206.00  
  Purchase #6 $160.98   7.687%   $173.3545   $173.35   $173.35   $173.40  
  Purchase #7 $152.63   13.494%   $173.2259   $173.23   $173.25   $173.20  
  7 purchase totals = $1,147.31       $1,234.4555   $1,234.47   $1,234.50   $1,234.50