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 $248.39   11.450%   $276.8307   $276.83   $276.85   $276.80  
  Purchase #2 $240.92   13.121%   $272.5311   $272.53   $272.55   $272.50  
  Purchase #3 $19.89   5.263%   $20.9368   $20.94   $20.95   $20.90  
  Purchase #4 $216.70   5.565%   $228.7594   $228.76   $228.75   $228.80  
  Purchase #5 $246.70   12.827%   $278.3442   $278.34   $278.35   $278.30  
  Purchase #6 $236.76   3.323%   $244.6275   $244.63   $244.65   $244.60  
  Purchase #7 $105.54   6.451%   $112.3484   $112.35   $112.35   $112.30  
  7 purchase totals = $1,314.90       $1,434.3781   $1,434.38   $1,434.45   $1,434.20