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	$113.49	4.308%	$118.3791	$118.38	$118.40	$118.40
Purchase #2	$35.82	12.855%	$40.4247	$40.42	$40.40	$40.40
Purchase #3	$46.76	7.643%	$50.3339	$50.33	$50.35	$50.30
Purchase #4	$33.63	11.458%	$37.4833	$37.48	$37.50	$37.50
Purchase #5	$55.31	8.812%	$60.1839	$60.18	$60.20	$60.20
Purchase #6	$85.72	13.568%	$97.3505	$97.35	$97.35	$97.40
Purchase #7	$55.42	7.806%	$59.7461	$59.75	$59.75	$59.70
7 purchase totals =	$426.15		$463.9015	$463.89	$463.95	$463.90