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	$250.97	13.125%	$283.9098	$283.91	$283.90	$283.90
Purchase #2	$26.25	3.164%	$27.0806	$27.08	$27.10	$27.10
Purchase #3	$234.38	3.792%	$243.2677	$243.27	$243.25	$243.30
Purchase #4	$53.53	7.176%	$57.3713	$57.37	$57.35	$57.40
Purchase #5	$189.44	10.739%	$209.784	$209.78	$209.80	$209.80
Purchase #6	$130.48	10.853%	$144.641	$144.64	$144.65	$144.60
Purchase #7	$120.76	5.378%	$127.2545	$127.25	$127.25	$127.30
7 purchase totals =	$1,005.81		$1,093.3089	$1,093.30	$1,093.30	$1,093.40