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	$71.67	12.766%	$80.8194	$80.82	$80.80	$80.80
Purchase #2	$224.77	11.465%	$250.5399	$250.54	$250.55	$250.50
Purchase #3	$163.64	10.282%	$180.4655	$180.47	$180.45	$180.50
Purchase #4	$165.79	13.826%	$188.7121	$188.71	$188.70	$188.70
Purchase #5	$68.78	5.116%	$72.2988	$72.30	$72.30	$72.30
Purchase #6	$19.30	12.587%	$21.7293	$21.73	$21.75	$21.70
Purchase #7	$68.51	5.348%	$72.1739	$72.17	$72.15	$72.20
7 purchase totals =	$782.46		$866.7389	$866.74	$866.70	$866.70