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	$70.53	6.300%	$74.9734	$74.97	$74.95	$75.00
Purchase #2	$38.60	4.343%	$40.2764	$40.28	$40.30	$40.30
Purchase #3	$6.86	4.744%	$7.1854	$7.19	$7.20	$7.20
Purchase #4	$136.30	5.228%	$143.4258	$143.43	$143.45	$143.40
Purchase #5	$147.56	9.182%	$161.109	$161.11	$161.10	$161.10
Purchase #6	$137.58	10.839%	$152.4923	$152.49	$152.50	$152.50
Purchase #7	$172.85	3.759%	$179.3474	$179.35	$179.35	$179.30
7 purchase totals =	$710.28		$758.8097	$758.82	$758.85	$758.80