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	$127.63	3.216%	$131.7346	$131.73	$131.75	$131.70
Purchase #2	$151.86	4.751%	$159.0749	$159.07	$159.05	$159.10
Purchase #3	$151.79	13.575%	$172.3955	$172.40	$172.40	$172.40
Purchase #4	$97.62	6.331%	$103.8003	$103.80	$103.80	$103.80
Purchase #5	$206.61	7.264%	$221.6182	$221.62	$221.60	$221.60
Purchase #6	$61.51	9.550%	$67.3842	$67.38	$67.40	$67.40
Purchase #7	$244.45	12.511%	$275.0331	$275.03	$275.05	$275.00
7 purchase totals =	$1,041.47		$1,131.0408	$1,131.03	$1,131.05	$1,131.00