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 $71.53   6.163%   $75.9384   $75.94   $75.95   $75.90  
  Purchase #2 $232.69   11.815%   $260.1823   $260.18   $260.20   $260.20  
  Purchase #3 $159.54   7.827%   $172.0272   $172.03   $172.05   $172.00  
  Purchase #4 $250.32   13.105%   $283.1244   $283.12   $283.10   $283.10  
  Purchase #5 $221.88   7.772%   $239.1245   $239.12   $239.10   $239.10  
  Purchase #6 $136.31   10.786%   $151.0124   $151.01   $151.00   $151.00  
  Purchase #7 $169.65   12.719%   $191.2278   $191.23   $191.25   $191.20  
  7 purchase totals = $1,241.92       $1,372.6370   $1,372.63   $1,372.65   $1,372.50