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 $209.91   10.615%   $232.1919   $232.19   $232.20   $232.20  
  Purchase #2 $226.72   6.577%   $241.6314   $241.63   $241.65   $241.60  
  Purchase #3 $237.37   12.381%   $266.7588   $266.76   $266.75   $266.80  
  Purchase #4 $56.54   10.475%   $62.4626   $62.46   $62.45   $62.50  
  Purchase #5 $151.64   12.814%   $171.0711   $171.07   $171.05   $171.10  
  Purchase #6 $9.30   7.106%   $9.9609   $9.96   $9.95   $10.00  
  Purchase #7 $68.88   13.782%   $78.373   $78.37   $78.35   $78.40  
  7 purchase totals = $960.36       $1,062.4497   $1,062.44   $1,062.40   $1,062.60