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	$72.54	8.130%	$78.4375	$78.44	$78.45	$78.40
Purchase #2	$125.89	13.662%	$143.0891	$143.09	$143.10	$143.10
Purchase #3	$72.81	10.345%	$80.3422	$80.34	$80.35	$80.30
Purchase #4	$188.62	8.202%	$204.0906	$204.09	$204.10	$204.10
Purchase #5	$21.99	7.137%	$23.5594	$23.56	$23.55	$23.60
Purchase #6	$99.45	11.690%	$111.0757	$111.08	$111.10	$111.10
Purchase #7	$198.46	9.468%	$217.2502	$217.25	$217.25	$217.30
7 purchase totals =	$779.76		$857.8447	$857.85	$857.90	$857.90