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	$238.73	3.487%	$247.0545	$247.05	$247.05	$247.10
Purchase #2	$18.57	12.397%	$20.8721	$20.87	$20.85	$20.90
Purchase #3	$11.72	9.297%	$12.8096	$12.81	$12.80	$12.80
Purchase #4	$101.70	8.609%	$110.4554	$110.46	$110.45	$110.50
Purchase #5	$19.25	6.494%	$20.5001	$20.50	$20.50	$20.50
Purchase #6	$124.81	13.798%	$142.0313	$142.03	$142.05	$142.00
Purchase #7	$96.52	9.377%	$105.5707	$105.57	$105.55	$105.60
7 purchase totals =	$611.30		$659.2937	$659.29	$659.25	$659.40