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 $232.49   6.183%   $246.8649   $246.86   $246.85   $246.90  
  Purchase #2 $233.71   9.349%   $255.5595   $255.56   $255.55   $255.60  
  Purchase #3 $160.25   5.671%   $169.3378   $169.34   $169.35   $169.30  
  Purchase #4 $227.51   12.110%   $255.0615   $255.06   $255.05   $255.10  
  Purchase #5 $227.87   9.469%   $249.447   $249.45   $249.45   $249.40  
  Purchase #6 $101.63   5.612%   $107.3335   $107.33   $107.35   $107.30  
  Purchase #7 $45.90   4.482%   $47.9572   $47.96   $47.95   $48.00  
  7 purchase totals = $1,229.36       $1,331.5614   $1,331.56   $1,331.55   $1,331.60