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 $217.95   10.724%   $241.323   $241.32   $241.30   $241.30  
  Purchase #2 $105.64   7.120%   $113.1616   $113.16   $113.15   $113.20  
  Purchase #3 $27.27   11.212%   $30.3275   $30.33   $30.35   $30.30  
  Purchase #4 $142.97   9.466%   $156.5035   $156.50   $156.50   $156.50  
  Purchase #5 $17.93   9.531%   $19.6389   $19.64   $19.65   $19.60  
  Purchase #6 $57.78   12.240%   $64.8523   $64.85   $64.85   $64.90  
  Purchase #7 $165.40   7.745%   $178.2102   $178.21   $178.20   $178.20  
  7 purchase totals = $734.94       $804.0170   $804.01   $804.00   $804.00