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	$103.35	5.365%	$108.8947	$108.89	$108.90	$108.90
Purchase #2	$116.64	10.783%	$129.2173	$129.22	$129.20	$129.20
Purchase #3	$199.56	11.467%	$222.4435	$222.44	$222.45	$222.40
Purchase #4	$239.96	5.827%	$253.9425	$253.94	$253.95	$253.90
Purchase #5	$160.56	5.680%	$169.6798	$169.68	$169.70	$169.70
Purchase #6	$114.59	8.114%	$123.8878	$123.89	$123.90	$123.90
Purchase #7	$101.31	3.180%	$104.5317	$104.53	$104.55	$104.50
7 purchase totals =	$1,035.97		$1,112.5973	$1,112.59	$1,112.65	$1,112.50