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	$54.69	4.525%	$57.1647	$57.16	$57.15	$57.20
Purchase #2	$92.46	7.784%	$99.6571	$99.66	$99.65	$99.70
Purchase #3	$78.67	8.811%	$85.6016	$85.60	$85.60	$85.60
Purchase #4	$89.95	4.743%	$94.2163	$94.22	$94.20	$94.20
Purchase #5	$70.79	13.280%	$80.1909	$80.19	$80.20	$80.20
Purchase #6	$90.29	12.589%	$101.6566	$101.66	$101.65	$101.70
Purchase #7	$196.99	11.825%	$220.2841	$220.28	$220.30	$220.30
7 purchase totals =	$673.84		$738.7713	$738.77	$738.75	$738.90