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	$37.95	7.341%	$40.7359	$40.74	$40.75	$40.70
Purchase #2	$58.37	11.674%	$65.1841	$65.18	$65.20	$65.20
Purchase #3	$136.39	10.465%	$150.6632	$150.66	$150.65	$150.70
Purchase #4	$69.34	3.325%	$71.6456	$71.65	$71.65	$71.60
Purchase #5	$37.36	3.341%	$38.6082	$38.61	$38.60	$38.60
Purchase #6	$193.32	3.536%	$200.1558	$200.16	$200.15	$200.20
Purchase #7	$224.47	3.845%	$233.1009	$233.10	$233.10	$233.10
7 purchase totals =	$757.20		$800.0937	$800.10	$800.10	$800.10