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 $59.86   3.646%   $62.0425   $62.04   $62.05   $62.00  
  Purchase #2 $47.37   6.859%   $50.6191   $50.62   $50.60   $50.60  
  Purchase #3 $28.76   12.531%   $32.3639   $32.36   $32.35   $32.40  
  Purchase #4 $167.85   7.727%   $180.8198   $180.82   $180.80   $180.80  
  Purchase #5 $138.37   13.541%   $157.1067   $157.11   $157.10   $157.10  
  Purchase #6 $230.54   13.817%   $262.3937   $262.39   $262.40   $262.40  
  Purchase #7 $15.97   5.514%   $16.8506   $16.85   $16.85   $16.90  
  7 purchase totals = $688.72       $762.1963   $762.19   $762.15   $762.20