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	$33.31	5.453%	$35.1264	$35.13	$35.15	$35.10
Purchase #2	$102.40	3.193%	$105.6696	$105.67	$105.65	$105.70
Purchase #3	$171.79	11.622%	$191.7554	$191.76	$191.75	$191.80
Purchase #4	$12.62	5.253%	$13.2829	$13.28	$13.30	$13.30
Purchase #5	$11.67	10.339%	$12.8766	$12.88	$12.90	$12.90
Purchase #6	$70.38	4.447%	$73.5098	$73.51	$73.50	$73.50
Purchase #7	$123.35	13.765%	$140.3291	$140.33	$140.35	$140.30
7 purchase totals =	$525.52		$572.5498	$572.56	$572.60	$572.60