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 $69.48   3.757%   $72.0904   $72.09   $72.10   $72.10  
  Purchase #2 $85.38   6.293%   $90.753   $90.75   $90.75   $90.80  
  Purchase #3 $175.47   4.121%   $182.7011   $182.70   $182.70   $182.70  
  Purchase #4 $42.27   6.114%   $44.8544   $44.85   $44.85   $44.90  
  Purchase #5 $49.97   13.396%   $56.664   $56.66   $56.65   $56.70  
  Purchase #6 $25.84   6.647%   $27.5576   $27.56   $27.55   $27.60  
  Purchase #7 $123.71   4.846%   $129.705   $129.71   $129.70   $129.70  
  7 purchase totals = $572.12       $604.3255   $604.32   $604.30   $604.50