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 $223.98   13.874%   $255.055   $255.06   $255.05   $255.10  
  Purchase #2 $114.85   8.467%   $124.5743   $124.57   $124.55   $124.60  
  Purchase #3 $105.79   4.405%   $110.45   $110.45   $110.45   $110.50  
  Purchase #4 $67.70   3.135%   $69.8224   $69.82   $69.80   $69.80  
  Purchase #5 $84.60   11.874%   $94.6454   $94.65   $94.65   $94.60  
  Purchase #6 $114.63   8.501%   $124.3747   $124.37   $124.35   $124.40  
  Purchase #7 $91.60   7.661%   $98.6175   $98.62   $98.60   $98.60  
  7 purchase totals = $803.15       $877.5393   $877.54   $877.45   $877.60