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	$44.89	5.383%	$47.3064	$47.31	$47.30	$47.30
Purchase #2	$31.59	11.757%	$35.304	$35.30	$35.30	$35.30
Purchase #3	$51.43	7.471%	$55.2723	$55.27	$55.25	$55.30
Purchase #4	$200.72	13.856%	$228.5318	$228.53	$228.55	$228.50
Purchase #5	$72.40	3.130%	$74.6661	$74.67	$74.65	$74.70
Purchase #6	$49.28	9.459%	$53.9414	$53.94	$53.95	$53.90
Purchase #7	$228.59	7.731%	$246.2623	$246.26	$246.25	$246.30
7 purchase totals =	$678.90		$741.2843	$741.28	$741.25	$741.30