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	$78.97	11.639%	$88.1613	$88.16	$88.15	$88.20
Purchase #2	$99.86	4.624%	$104.4775	$104.48	$104.50	$104.50
Purchase #3	$136.82	3.132%	$141.1052	$141.11	$141.10	$141.10
Purchase #4	$36.82	11.421%	$41.0252	$41.03	$41.05	$41.00
Purchase #5	$118.86	6.361%	$126.4207	$126.42	$126.40	$126.40
Purchase #6	$33.92	4.438%	$35.4254	$35.43	$35.45	$35.40
Purchase #7	$159.26	9.748%	$174.7847	$174.78	$174.80	$174.80
7 purchase totals =	$664.51		$711.4000	$711.41	$711.45	$711.40