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	$238.52	10.303%	$263.0947	$263.09	$263.10	$263.10
Purchase #2	$126.93	7.843%	$136.8851	$136.89	$136.90	$136.90
Purchase #3	$133.77	5.742%	$141.4511	$141.45	$141.45	$141.50
Purchase #4	$110.33	7.592%	$118.7063	$118.71	$118.70	$118.70
Purchase #5	$205.82	9.568%	$225.5129	$225.51	$225.50	$225.50
Purchase #6	$71.72	10.178%	$79.0197	$79.02	$79.00	$79.00
Purchase #7	$146.40	13.697%	$166.4524	$166.45	$166.45	$166.50
7 purchase totals =	$1,033.49		$1,131.1222	$1,131.12	$1,131.10	$1,131.20