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	$235.26	8.183%	$254.5113	$254.51	$254.50	$254.50
Purchase #2	$31.41	12.578%	$35.3607	$35.36	$35.35	$35.40
Purchase #3	$80.51	10.108%	$88.648	$88.65	$88.65	$88.60
Purchase #4	$91.26	10.166%	$100.5375	$100.54	$100.55	$100.50
Purchase #5	$51.58	4.479%	$53.8903	$53.89	$53.90	$53.90
Purchase #6	$154.47	4.684%	$161.7054	$161.71	$161.70	$161.70
Purchase #7	$131.55	9.577%	$144.1485	$144.15	$144.15	$144.10
7 purchase totals =	$776.04		$838.8017	$838.81	$838.80	$838.70