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	$44.45	13.720%	$50.5485	$50.55	$50.55	$50.50
Purchase #2	$135.30	9.515%	$148.1738	$148.17	$148.15	$148.20
Purchase #3	$11.40	13.299%	$12.9161	$12.92	$12.90	$12.90
Purchase #4	$244.56	8.668%	$265.7585	$265.76	$265.75	$265.80
Purchase #5	$168.69	13.250%	$191.0414	$191.04	$191.05	$191.00
Purchase #6	$179.72	11.400%	$200.2081	$200.21	$200.20	$200.20
Purchase #7	$50.36	3.151%	$51.9468	$51.95	$51.95	$51.90
7 purchase totals =	$834.48		$920.5932	$920.60	$920.55	$920.50