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	$115.51	3.155%	$119.1543	$119.15	$119.15	$119.20
Purchase #2	$184.71	13.434%	$209.5239	$209.52	$209.50	$209.50
Purchase #3	$108.90	11.428%	$121.3451	$121.35	$121.35	$121.30
Purchase #4	$35.30	6.280%	$37.5168	$37.52	$37.50	$37.50
Purchase #5	$134.88	13.673%	$153.3221	$153.32	$153.30	$153.30
Purchase #6	$142.94	10.850%	$158.449	$158.45	$158.45	$158.40
Purchase #7	$225.60	11.472%	$251.4808	$251.48	$251.50	$251.50
7 purchase totals =	$947.84		$1,050.7920	$1,050.79	$1,050.75	$1,050.70