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 $207.87   12.122%   $233.068   $233.07   $233.05   $233.10  
  Purchase #2 $25.89   3.618%   $26.8267   $26.83   $26.85   $26.80  
  Purchase #3 $26.49   9.369%   $28.9718   $28.97   $28.95   $29.00  
  Purchase #4 $10.85   5.532%   $11.4502   $11.45   $11.45   $11.50  
  Purchase #5 $238.95   4.293%   $249.2081   $249.21   $249.20   $249.20  
  Purchase #6 $161.70   11.195%   $179.8023   $179.80   $179.80   $179.80  
  Purchase #7 $245.71   7.494%   $264.1235   $264.12   $264.10   $264.10  
  7 purchase totals = $917.46       $993.4506   $993.45   $993.40   $993.50