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	$35.32	6.861%	$37.7433	$37.74	$37.75	$37.70
Purchase #2	$102.87	7.320%	$110.4001	$110.40	$110.40	$110.40
Purchase #3	$132.46	5.623%	$139.9082	$139.91	$139.90	$139.90
Purchase #4	$54.37	10.822%	$60.2539	$60.25	$60.25	$60.30
Purchase #5	$212.79	4.520%	$222.4081	$222.41	$222.40	$222.40
Purchase #6	$38.27	6.802%	$40.8731	$40.87	$40.85	$40.90
Purchase #7	$77.35	13.469%	$87.7683	$87.77	$87.75	$87.80
7 purchase totals =	$653.43		$699.3550	$699.35	$699.30	$699.40