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	$165.55	4.335%	$172.7266	$172.73	$172.75	$172.70
Purchase #2	$86.40	6.202%	$91.7585	$91.76	$91.75	$91.80
Purchase #3	$41.26	4.827%	$43.2516	$43.25	$43.25	$43.30
Purchase #4	$166.77	11.220%	$185.4816	$185.48	$185.50	$185.50
Purchase #5	$38.76	12.843%	$43.7379	$43.74	$43.75	$43.70
Purchase #6	$64.30	10.633%	$71.137	$71.14	$71.15	$71.10
Purchase #7	$32.80	6.859%	$35.0498	$35.05	$35.05	$35.00
7 purchase totals =	$595.84		$643.1430	$643.15	$643.20	$643.10