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 $131.39   4.651%   $137.5009   $137.50   $137.50   $137.50  
  Purchase #2 $13.94   4.676%   $14.5918   $14.59   $14.60   $14.60  
  Purchase #3 $71.40   7.554%   $76.7936   $76.79   $76.80   $76.80  
  Purchase #4 $58.84   9.799%   $64.6057   $64.61   $64.60   $64.60  
  Purchase #5 $198.99   5.375%   $209.6857   $209.69   $209.70   $209.70  
  Purchase #6 $135.60   4.493%   $141.6925   $141.69   $141.70   $141.70  
  Purchase #7 $219.58   3.568%   $227.4146   $227.41   $227.40   $227.40  
  7 purchase totals = $829.74       $872.2848   $872.28   $872.30   $872.30