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 $61.25   5.581%   $64.6684   $64.67   $64.65   $64.70  
  Purchase #2 $99.79   10.535%   $110.3029   $110.30   $110.30   $110.30  
  Purchase #3 $123.69   11.626%   $138.0702   $138.07   $138.05   $138.10  
  Purchase #4 $50.98   9.719%   $55.9347   $55.93   $55.95   $55.90  
  Purchase #5 $45.94   6.725%   $49.0295   $49.03   $49.05   $49.00  
  Purchase #6 $231.67   5.542%   $244.5092   $244.51   $244.50   $244.50  
  Purchase #7 $250.45   12.639%   $282.1044   $282.10   $282.10   $282.10  
  7 purchase totals = $863.77       $944.6193   $944.61   $944.60   $944.60