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	$79.86	7.561%	$85.8982	$85.90	$85.90	$85.90
Purchase #2	$101.79	9.772%	$111.7369	$111.74	$111.75	$111.70
Purchase #3	$227.47	6.711%	$242.7355	$242.74	$242.75	$242.70
Purchase #4	$115.99	9.569%	$127.0891	$127.09	$127.10	$127.10
Purchase #5	$140.70	11.200%	$156.4584	$156.46	$156.45	$156.50
Purchase #6	$113.45	8.463%	$123.0513	$123.05	$123.05	$123.10
Purchase #7	$47.80	6.207%	$50.7669	$50.77	$50.75	$50.80
7 purchase totals =	$827.06		$897.7363	$897.75	$897.75	$897.80