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 $250.78   6.475%   $267.018   $267.02   $267.00   $267.00  
  Purchase #2 $13.84   10.548%   $15.2998   $15.30   $15.30   $15.30  
  Purchase #3 $95.88   11.866%   $107.2571   $107.26   $107.25   $107.30  
  Purchase #4 $77.85   11.622%   $86.8977   $86.90   $86.90   $86.90  
  Purchase #5 $97.45   6.623%   $103.9041   $103.90   $103.90   $103.90  
  Purchase #6 $242.55   11.359%   $270.1013   $270.10   $270.10   $270.10  
  Purchase #7 $96.38   12.479%   $108.4073   $108.41   $108.40   $108.40  
  7 purchase totals = $874.73       $958.8853   $958.89   $958.85   $958.90