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 $234.25   6.576%   $249.6543   $249.65   $249.65   $249.70  
  Purchase #2 $65.79   6.261%   $69.9091   $69.91   $69.90   $69.90  
  Purchase #3 $170.60   9.130%   $186.1758   $186.18   $186.20   $186.20  
  Purchase #4 $32.73   5.781%   $34.6221   $34.62   $34.60   $34.60  
  Purchase #5 $230.60   4.254%   $240.4097   $240.41   $240.40   $240.40  
  Purchase #6 $67.99   10.325%   $75.01   $75.01   $75.00   $75.00  
  Purchase #7 $242.30   8.451%   $262.7768   $262.78   $262.80   $262.80  
  7 purchase totals = $1,044.26       $1,118.5578   $1,118.56   $1,118.55   $1,118.60