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 $41.25   6.114%   $43.772   $43.77   $43.75   $43.80  
  Purchase #2 $245.77   3.138%   $253.4823   $253.48   $253.50   $253.50  
  Purchase #3 $151.80   12.323%   $170.5063   $170.51   $170.50   $170.50  
  Purchase #4 $119.78   11.827%   $133.9464   $133.95   $133.95   $133.90  
  Purchase #5 $246.69   6.783%   $263.423   $263.42   $263.40   $263.40  
  Purchase #6 $59.49   8.703%   $64.6674   $64.67   $64.65   $64.70  
  Purchase #7 $100.48   10.179%   $110.7079   $110.71   $110.70   $110.70  
  7 purchase totals = $965.26       $1,040.5053   $1,040.51   $1,040.45   $1,040.50