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	$65.44	13.787%	$74.4622	$74.46	$74.45	$74.50
Purchase #2	$104.30	6.708%	$111.2964	$111.30	$111.30	$111.30
Purchase #3	$150.74	11.650%	$168.3012	$168.30	$168.30	$168.30
Purchase #4	$66.48	6.635%	$70.8909	$70.89	$70.90	$70.90
Purchase #5	$112.69	7.221%	$120.8273	$120.83	$120.85	$120.80
Purchase #6	$189.58	7.501%	$203.8004	$203.80	$203.80	$203.80
Purchase #7	$48.80	3.163%	$50.3435	$50.34	$50.35	$50.30
7 purchase totals =	$738.03		$799.9219	$799.92	$799.95	$799.90