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 $72.66   12.118%   $81.4649   $81.46   $81.45   $81.50  
  Purchase #2 $32.98   5.247%   $34.7105   $34.71   $34.70   $34.70  
  Purchase #3 $80.80   4.217%   $84.2073   $84.21   $84.20   $84.20  
  Purchase #4 $139.37   9.812%   $153.045   $153.05   $153.05   $153.00  
  Purchase #5 $183.76   5.851%   $194.5118   $194.51   $194.50   $194.50  
  Purchase #6 $228.41   11.730%   $255.2025   $255.20   $255.20   $255.20  
  Purchase #7 $243.39   7.409%   $261.4228   $261.42   $261.40   $261.40  
  7 purchase totals = $981.37       $1,064.5648   $1,064.56   $1,064.50   $1,064.50