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	$77.81	7.208%	$83.4185	$83.42	$83.40	$83.40
Purchase #2	$226.91	5.719%	$239.887	$239.89	$239.90	$239.90
Purchase #3	$121.78	12.640%	$137.173	$137.17	$137.15	$137.20
Purchase #4	$139.98	7.816%	$150.9208	$150.92	$150.90	$150.90
Purchase #5	$35.48	11.615%	$39.601	$39.60	$39.60	$39.60
Purchase #6	$44.27	3.798%	$45.9514	$45.95	$45.95	$46.00
Purchase #7	$177.50	4.539%	$185.5567	$185.56	$185.55	$185.60
7 purchase totals =	$823.73		$882.5084	$882.51	$882.45	$882.60