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	$220.53	13.409%	$250.1009	$250.10	$250.10	$250.10
Purchase #2	$83.68	8.445%	$90.7468	$90.75	$90.75	$90.70
Purchase #3	$41.52	8.766%	$45.1596	$45.16	$45.15	$45.20
Purchase #4	$34.35	3.217%	$35.455	$35.46	$35.45	$35.50
Purchase #5	$119.36	7.271%	$128.0387	$128.04	$128.05	$128.00
Purchase #6	$190.73	3.111%	$196.6636	$196.66	$196.65	$196.70
Purchase #7	$78.95	11.757%	$88.2322	$88.23	$88.25	$88.20
7 purchase totals =	$769.12		$834.3968	$834.40	$834.40	$834.40