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 $16.94   13.568%   $19.2384   $19.24   $19.25   $19.20  
  Purchase #2 $56.41   10.267%   $62.2016   $62.20   $62.20   $62.20  
  Purchase #3 $153.80   8.751%   $167.259   $167.26   $167.25   $167.30  
  Purchase #4 $73.57   10.787%   $81.506   $81.51   $81.50   $81.50  
  Purchase #5 $140.64   12.275%   $157.9036   $157.90   $157.90   $157.90  
  Purchase #6 $6.99   11.590%   $7.8001   $7.80   $7.80   $7.80  
  Purchase #7 $225.98   10.320%   $249.3011   $249.30   $249.30   $249.30  
  7 purchase totals = $674.33       $745.2098   $745.21   $745.20   $745.20