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	$11.74	9.375%	$12.8406	$12.84	$12.85	$12.80
Purchase #2	$112.87	11.134%	$125.4369	$125.44	$125.45	$125.40
Purchase #3	$79.64	12.323%	$89.454	$89.45	$89.45	$89.50
Purchase #4	$232.62	4.574%	$243.26	$243.26	$243.25	$243.30
Purchase #5	$35.55	8.595%	$38.6055	$38.61	$38.60	$38.60
Purchase #6	$5.61	9.341%	$6.134	$6.13	$6.15	$6.10
Purchase #7	$80.79	11.242%	$89.8724	$89.87	$89.85	$89.90
7 purchase totals =	$558.82		$605.6034	$605.60	$605.60	$605.60