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 $227.73   7.814%   $245.5248   $245.52   $245.50   $245.50  
  Purchase #2 $241.40   10.442%   $266.607   $266.61   $266.60   $266.60  
  Purchase #3 $224.37   11.508%   $250.1905   $250.19   $250.20   $250.20  
  Purchase #4 $166.59   11.817%   $186.2759   $186.28   $186.30   $186.30  
  Purchase #5 $171.96   7.557%   $184.955   $184.96   $184.95   $185.00  
  Purchase #6 $249.62   4.647%   $261.2198   $261.22   $261.20   $261.20  
  Purchase #7 $8.42   13.128%   $9.5254   $9.53   $9.55   $9.50  
  7 purchase totals = $1,290.09       $1,404.2984   $1,404.31   $1,404.30   $1,404.30