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	$44.69	13.145%	$50.5645	$50.56	$50.55	$50.60
Purchase #2	$212.91	12.170%	$238.8211	$238.82	$238.80	$238.80
Purchase #3	$240.42	5.799%	$254.362	$254.36	$254.35	$254.40
Purchase #4	$189.92	3.584%	$196.7267	$196.73	$196.75	$196.70
Purchase #5	$83.90	12.843%	$94.6753	$94.68	$94.70	$94.70
Purchase #6	$180.80	7.741%	$194.7957	$194.80	$194.80	$194.80
Purchase #7	$29.85	11.774%	$33.3645	$33.36	$33.35	$33.40
7 purchase totals =	$982.49		$1,063.3098	$1,063.31	$1,063.30	$1,063.40