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 $109.62   4.242%   $114.2701   $114.27   $114.25   $114.30  
  Purchase #2 $228.67   5.277%   $240.7369   $240.74   $240.75   $240.70  
  Purchase #3 $50.80   8.648%   $55.1932   $55.19   $55.20   $55.20  
  Purchase #4 $91.47   11.104%   $101.6268   $101.63   $101.65   $101.60  
  Purchase #5 $119.60   7.145%   $128.1454   $128.15   $128.15   $128.10  
  Purchase #6 $24.79   11.124%   $27.5476   $27.55   $27.55   $27.50  
  Purchase #7 $77.69   13.300%   $88.0228   $88.02   $88.00   $88.00  
  7 purchase totals = $702.64       $755.5428   $755.55   $755.55   $755.40