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 $176.95   6.259%   $188.0253   $188.03   $188.05   $188.00  
  Purchase #2 $119.51   9.322%   $130.6507   $130.65   $130.65   $130.70  
  Purchase #3 $131.56   10.451%   $145.3093   $145.31   $145.30   $145.30  
  Purchase #4 $94.67   8.423%   $102.6441   $102.64   $102.65   $102.60  
  Purchase #5 $76.41   3.387%   $78.998   $79.00   $79.00   $79.00  
  Purchase #6 $221.85   7.762%   $239.07   $239.07   $239.05   $239.10  
  Purchase #7 $70.75   5.279%   $74.4849   $74.48   $74.50   $74.50  
  7 purchase totals = $891.70       $959.1823   $959.18   $959.20   $959.20