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 $229.42   10.397%   $253.2728   $253.27   $253.25   $253.30  
  Purchase #2 $61.37   6.840%   $65.5677   $65.57   $65.55   $65.60  
  Purchase #3 $56.94   9.608%   $62.4108   $62.41   $62.40   $62.40  
  Purchase #4 $116.54   8.191%   $126.0858   $126.09   $126.10   $126.10  
  Purchase #5 $246.66   10.769%   $273.2228   $273.22   $273.20   $273.20  
  Purchase #6 $68.83   11.668%   $76.8611   $76.86   $76.85   $76.90  
  Purchase #7 $185.62   7.485%   $199.5137   $199.51   $199.50   $199.50  
  7 purchase totals = $965.38       $1,056.9347   $1,056.93   $1,056.85   $1,057.00