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 $86.38   13.377%   $97.9351   $97.94   $97.95   $97.90  
  Purchase #2 $49.74   7.565%   $53.5028   $53.50   $53.50   $53.50  
  Purchase #3 $212.96   8.319%   $230.6761   $230.68   $230.70   $230.70  
  Purchase #4 $242.97   7.319%   $260.753   $260.75   $260.75   $260.80  
  Purchase #5 $150.29   10.361%   $165.8615   $165.86   $165.85   $165.90  
  Purchase #6 $45.77   3.773%   $47.4969   $47.50   $47.50   $47.50  
  Purchase #7 $46.73   10.571%   $51.6698   $51.67   $51.65   $51.70  
  7 purchase totals = $834.84       $907.8952   $907.90   $907.90   $908.00