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	$74.53	13.414%	$84.5275	$84.53	$84.55	$84.50
Purchase #2	$156.56	3.665%	$162.2979	$162.30	$162.30	$162.30
Purchase #3	$185.54	3.296%	$191.6554	$191.66	$191.65	$191.70
Purchase #4	$88.33	3.611%	$91.5196	$91.52	$91.50	$91.50
Purchase #5	$161.70	8.485%	$175.4202	$175.42	$175.40	$175.40
Purchase #6	$165.81	3.414%	$171.4708	$171.47	$171.45	$171.50
Purchase #7	$106.90	7.111%	$114.5017	$114.50	$114.50	$114.50
7 purchase totals =	$939.37		$991.3931	$991.40	$991.35	$991.40