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 $27.86   5.546%   $29.4051   $29.41   $29.40   $29.40  
  Purchase #2 $184.37   5.182%   $193.9241   $193.92   $193.90   $193.90  
  Purchase #3 $69.76   5.530%   $73.6177   $73.62   $73.60   $73.60  
  Purchase #4 $150.42   6.107%   $159.6061   $159.61   $159.60   $159.60  
  Purchase #5 $62.35   9.849%   $68.4909   $68.49   $68.50   $68.50  
  Purchase #6 $118.73   13.677%   $134.9687   $134.97   $134.95   $135.00  
  Purchase #7 $127.29   3.406%   $131.6255   $131.63   $131.65   $131.60  
  7 purchase totals = $740.78       $791.6381   $791.65   $791.60   $791.60