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 $61.94   5.790%   $65.5263   $65.53   $65.55   $65.50  
  Purchase #2 $170.57   6.423%   $181.5257   $181.53   $181.55   $181.50  
  Purchase #3 $182.54   12.667%   $205.6623   $205.66   $205.65   $205.70  
  Purchase #4 $53.77   12.137%   $60.2961   $60.30   $60.30   $60.30  
  Purchase #5 $115.42   9.275%   $126.1252   $126.13   $126.15   $126.10  
  Purchase #6 $187.98   10.775%   $208.2348   $208.23   $208.25   $208.20  
  Purchase #7 $100.61   6.840%   $107.4917   $107.49   $107.50   $107.50  
  7 purchase totals = $872.83       $954.8621   $954.87   $954.95   $954.80