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	$70.91	3.700%	$73.5337	$73.53	$73.55	$73.50
Purchase #2	$92.91	8.442%	$100.7535	$100.75	$100.75	$100.80
Purchase #3	$152.78	8.247%	$165.3798	$165.38	$165.40	$165.40
Purchase #4	$91.65	12.751%	$103.3363	$103.34	$103.35	$103.30
Purchase #5	$112.26	3.674%	$116.3844	$116.38	$116.40	$116.40
Purchase #6	$38.73	9.404%	$42.3722	$42.37	$42.35	$42.40
Purchase #7	$114.68	10.558%	$126.7879	$126.79	$126.80	$126.80
7 purchase totals =	$673.92		$728.5478	$728.54	$728.60	$728.60