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	$179.80	9.221%	$196.3794	$196.38	$196.40	$196.40
Purchase #2	$57.62	13.872%	$65.613	$65.61	$65.60	$65.60
Purchase #3	$69.39	11.239%	$77.1887	$77.19	$77.20	$77.20
Purchase #4	$177.41	8.534%	$192.5502	$192.55	$192.55	$192.60
Purchase #5	$86.57	6.546%	$92.2369	$92.24	$92.25	$92.20
Purchase #6	$6.33	11.143%	$7.0354	$7.04	$7.05	$7.00
Purchase #7	$42.78	9.618%	$46.8946	$46.89	$46.90	$46.90
7 purchase totals =	$619.90		$677.8982	$677.90	$677.95	$677.90