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	$170.28	10.633%	$188.3859	$188.39	$188.40	$188.40
Purchase #2	$26.86	8.116%	$29.04	$29.04	$29.05	$29.00
Purchase #3	$197.46	13.126%	$223.3786	$223.38	$223.40	$223.40
Purchase #4	$110.91	12.180%	$124.4188	$124.42	$124.40	$124.40
Purchase #5	$188.78	3.459%	$195.3099	$195.31	$195.30	$195.30
Purchase #6	$225.43	10.601%	$249.3278	$249.33	$249.35	$249.30
Purchase #7	$94.43	6.454%	$100.5245	$100.52	$100.50	$100.50
7 purchase totals =	$1,014.15		$1,110.3855	$1,110.39	$1,110.40	$1,110.30