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	$65.38	7.847%	$70.5104	$70.51	$70.50	$70.50
Purchase #2	$133.41	10.427%	$147.3207	$147.32	$147.30	$147.30
Purchase #3	$40.41	11.845%	$45.1966	$45.20	$45.20	$45.20
Purchase #4	$75.30	7.258%	$80.7653	$80.77	$80.75	$80.80
Purchase #5	$135.94	7.862%	$146.6276	$146.63	$146.65	$146.60
Purchase #6	$31.26	13.203%	$35.3873	$35.39	$35.40	$35.40
Purchase #7	$160.69	11.578%	$179.2947	$179.29	$179.30	$179.30
7 purchase totals =	$642.39		$705.1026	$705.11	$705.10	$705.10