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	$40.38	4.807%	$42.3211	$42.32	$42.30	$42.30
Purchase #2	$80.60	9.822%	$88.5165	$88.52	$88.50	$88.50
Purchase #3	$31.51	3.691%	$32.673	$32.67	$32.65	$32.70
Purchase #4	$241.26	5.164%	$253.7187	$253.72	$253.70	$253.70
Purchase #5	$237.30	6.799%	$253.434	$253.43	$253.45	$253.40
Purchase #6	$17.86	3.747%	$18.5292	$18.53	$18.55	$18.50
Purchase #7	$204.84	3.847%	$212.7202	$212.72	$212.70	$212.70
7 purchase totals =	$853.75		$901.9127	$901.91	$901.85	$901.80