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 $234.40   13.733%   $266.5902   $266.59   $266.60   $266.60  
  Purchase #2 $94.34   12.781%   $106.3976   $106.40   $106.40   $106.40  
  Purchase #3 $32.30   9.307%   $35.3062   $35.31   $35.30   $35.30  
  Purchase #4 $219.61   10.462%   $242.5856   $242.59   $242.60   $242.60  
  Purchase #5 $97.28   10.284%   $107.2843   $107.28   $107.30   $107.30  
  Purchase #6 $249.67   8.503%   $270.8994   $270.90   $270.90   $270.90  
  Purchase #7 $12.51   11.408%   $13.9371   $13.94   $13.95   $13.90  
  7 purchase totals = $940.11       $1,043.0004   $1,043.01   $1,043.05   $1,043.00