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 $42.25   3.312%   $43.6493   $43.65   $43.65   $43.60  
  Purchase #2 $101.69   10.454%   $112.3207   $112.32   $112.30   $112.30  
  Purchase #3 $249.43   9.735%   $273.712   $273.71   $273.70   $273.70  
  Purchase #4 $197.93   10.370%   $218.4553   $218.46   $218.45   $218.50  
  Purchase #5 $107.95   13.271%   $122.276   $122.28   $122.30   $122.30  
  Purchase #6 $238.62   12.499%   $268.4451   $268.45   $268.45   $268.40  
  Purchase #7 $5.64   12.808%   $6.3624   $6.36   $6.35   $6.40  
  7 purchase totals = $943.51       $1,045.2208   $1,045.23   $1,045.20   $1,045.20