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	$96.46	13.628%	$109.6056	$109.61	$109.60	$109.60
Purchase #2	$113.73	8.863%	$123.8099	$123.81	$123.80	$123.80
Purchase #3	$185.45	3.384%	$191.7256	$191.73	$191.75	$191.70
Purchase #4	$91.43	6.802%	$97.6491	$97.65	$97.65	$97.60
Purchase #5	$141.77	4.520%	$148.178	$148.18	$148.20	$148.20
Purchase #6	$5.94	3.668%	$6.1579	$6.16	$6.15	$6.20
Purchase #7	$88.76	13.314%	$100.5775	$100.58	$100.60	$100.60
7 purchase totals =	$723.54		$777.7036	$777.72	$777.75	$777.70