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	$172.93	13.109%	$195.5994	$195.60	$195.60	$195.60
Purchase #2	$85.65	4.360%	$89.3843	$89.38	$89.40	$89.40
Purchase #3	$116.45	6.234%	$123.7095	$123.71	$123.70	$123.70
Purchase #4	$169.40	9.142%	$184.8865	$184.89	$184.90	$184.90
Purchase #5	$134.97	10.530%	$149.1823	$149.18	$149.20	$149.20
Purchase #6	$53.96	3.106%	$55.636	$55.64	$55.65	$55.60
Purchase #7	$35.81	12.156%	$40.1631	$40.16	$40.15	$40.20
7 purchase totals =	$769.17		$838.5611	$838.56	$838.60	$838.60