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	$247.96	12.560%	$279.1038	$279.10	$279.10	$279.10
Purchase #2	$101.68	9.803%	$111.6477	$111.65	$111.65	$111.60
Purchase #3	$83.36	13.232%	$94.3902	$94.39	$94.40	$94.40
Purchase #4	$39.50	6.848%	$42.205	$42.21	$42.20	$42.20
Purchase #5	$166.74	13.744%	$189.6567	$189.66	$189.65	$189.70
Purchase #6	$130.75	12.730%	$147.3945	$147.39	$147.40	$147.40
Purchase #7	$180.79	5.452%	$190.6467	$190.65	$190.65	$190.60
7 purchase totals =	$950.78		$1,055.0446	$1,055.05	$1,055.05	$1,055.00