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	$9.51	7.651%	$10.2376	$10.24	$10.25	$10.20
Purchase #2	$28.71	12.820%	$32.3906	$32.39	$32.40	$32.40
Purchase #3	$155.82	3.158%	$160.7408	$160.74	$160.75	$160.70
Purchase #4	$118.88	11.282%	$132.292	$132.29	$132.30	$132.30
Purchase #5	$88.89	4.329%	$92.738	$92.74	$92.75	$92.70
Purchase #6	$153.32	4.702%	$160.5291	$160.53	$160.55	$160.50
Purchase #7	$54.46	5.697%	$57.5626	$57.56	$57.55	$57.60
7 purchase totals =	$609.59		$646.4907	$646.49	$646.55	$646.40