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 $53.98   9.160%   $58.9246   $58.92   $58.90   $58.90  
  Purchase #2 $204.98   4.763%   $214.7432   $214.74   $214.75   $214.70  
  Purchase #3 $85.80   7.157%   $91.9407   $91.94   $91.95   $91.90  
  Purchase #4 $226.37   3.349%   $233.9511   $233.95   $233.95   $234.00  
  Purchase #5 $82.91   6.696%   $88.4617   $88.46   $88.45   $88.50  
  Purchase #6 $70.98   8.336%   $76.8969   $76.90   $76.90   $76.90  
  Purchase #7 $17.48   12.240%   $19.6196   $19.62   $19.60   $19.60  
  7 purchase totals = $742.50       $784.5378   $784.53   $784.50   $784.50