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 $29.98   7.482%   $32.2231   $32.22   $32.20   $32.20  
  Purchase #2 $154.77   9.227%   $169.0506   $169.05   $169.05   $169.10  
  Purchase #3 $32.66   5.167%   $34.3475   $34.35   $34.35   $34.30  
  Purchase #4 $118.73   3.225%   $122.559   $122.56   $122.55   $122.60  
  Purchase #5 $67.69   6.364%   $71.9978   $72.00   $72.00   $72.00  
  Purchase #6 $13.79   6.359%   $14.6669   $14.67   $14.65   $14.70  
  Purchase #7 $176.50   3.434%   $182.561   $182.56   $182.55   $182.60  
  7 purchase totals = $594.12       $627.4059   $627.41   $627.35   $627.50