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 $148.57   6.246%   $157.8497   $157.85   $157.85   $157.80  
  Purchase #2 $240.63   9.113%   $262.5586   $262.56   $262.55   $262.60  
  Purchase #3 $123.35   6.260%   $131.0717   $131.07   $131.05   $131.10  
  Purchase #4 $49.87   10.835%   $55.2734   $55.27   $55.25   $55.30  
  Purchase #5 $163.97   5.462%   $172.926   $172.93   $172.95   $172.90  
  Purchase #6 $172.71   6.530%   $183.988   $183.99   $184.00   $184.00  
  Purchase #7 $75.69   12.214%   $84.9348   $84.93   $84.95   $84.90  
  7 purchase totals = $974.79       $1,048.6022   $1,048.60   $1,048.60   $1,048.60