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	$52.43	7.799%	$56.519	$56.52	$56.50	$56.50
Purchase #2	$139.77	7.675%	$150.4973	$150.50	$150.50	$150.50
Purchase #3	$215.31	6.518%	$229.3439	$229.34	$229.35	$229.30
Purchase #4	$53.41	9.578%	$58.5256	$58.53	$58.55	$58.50
Purchase #5	$65.67	13.310%	$74.4107	$74.41	$74.40	$74.40
Purchase #6	$18.29	13.249%	$20.7132	$20.71	$20.70	$20.70
Purchase #7	$245.52	3.766%	$254.7663	$254.77	$254.75	$254.80
7 purchase totals =	$790.40		$844.7760	$844.78	$844.75	$844.70