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 $65.78   4.400%   $68.6743   $68.67   $68.65   $68.70  
  Purchase #2 $202.25   6.232%   $214.8542   $214.85   $214.85   $214.90  
  Purchase #3 $224.33   10.292%   $247.418   $247.42   $247.40   $247.40  
  Purchase #4 $222.25   3.118%   $229.1798   $229.18   $229.20   $229.20  
  Purchase #5 $87.30   8.597%   $94.8052   $94.81   $94.80   $94.80  
  Purchase #6 $45.62   12.523%   $51.333   $51.33   $51.35   $51.30  
  Purchase #7 $53.29   6.504%   $56.756   $56.76   $56.75   $56.80  
  7 purchase totals = $900.82       $963.0205   $963.02   $963.00   $963.10