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	$226.50	4.356%	$236.3663	$236.37	$236.35	$236.40
Purchase #2	$153.64	12.460%	$172.7835	$172.78	$172.80	$172.80
Purchase #3	$243.59	8.731%	$264.8578	$264.86	$264.85	$264.90
Purchase #4	$71.53	8.862%	$77.869	$77.87	$77.85	$77.90
Purchase #5	$137.84	12.847%	$155.5483	$155.55	$155.55	$155.50
Purchase #6	$112.46	13.741%	$127.9131	$127.91	$127.90	$127.90
Purchase #7	$82.40	9.851%	$90.5172	$90.52	$90.50	$90.50
7 purchase totals =	$1,027.96		$1,125.8552	$1,125.86	$1,125.80	$1,125.90