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 $186.52   3.242%   $192.567   $192.57   $192.55   $192.60  
  Purchase #2 $127.34   4.419%   $132.9672   $132.97   $132.95   $133.00  
  Purchase #3 $21.65   10.642%   $23.954   $23.95   $23.95   $24.00  
  Purchase #4 $27.75   6.578%   $29.5754   $29.58   $29.60   $29.60  
  Purchase #5 $215.44   13.416%   $244.3434   $244.34   $244.35   $244.30  
  Purchase #6 $133.28   6.558%   $142.0205   $142.02   $142.00   $142.00  
  Purchase #7 $183.40   8.788%   $199.5172   $199.52   $199.50   $199.50  
  7 purchase totals = $895.38       $964.9447   $964.95   $964.90   $965.00