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 $29.27   11.207%   $32.5503   $32.55   $32.55   $32.60  
  Purchase #2 $119.39   13.583%   $135.6067   $135.61   $135.60   $135.60  
  Purchase #3 $39.25   13.801%   $44.6669   $44.67   $44.65   $44.70  
  Purchase #4 $155.67   5.586%   $164.3657   $164.37   $164.35   $164.40  
  Purchase #5 $46.48   12.594%   $52.3337   $52.33   $52.35   $52.30  
  Purchase #6 $173.41   10.494%   $191.6076   $191.61   $191.60   $191.60  
  Purchase #7 $122.29   11.345%   $136.1638   $136.16   $136.15   $136.20  
  7 purchase totals = $685.76       $757.2947   $757.30   $757.25   $757.40