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	$37.65	9.425%	$41.1985	$41.20	$41.20	$41.20
Purchase #2	$43.96	3.512%	$45.5039	$45.50	$45.50	$45.50
Purchase #3	$125.30	10.119%	$137.9791	$137.98	$138.00	$138.00
Purchase #4	$59.76	4.606%	$62.5125	$62.51	$62.50	$62.50
Purchase #5	$54.37	8.224%	$58.8414	$58.84	$58.85	$58.80
Purchase #6	$39.61	9.521%	$43.3813	$43.38	$43.40	$43.40
Purchase #7	$91.72	11.251%	$102.0394	$102.04	$102.05	$102.00
7 purchase totals =	$452.37		$491.4561	$491.45	$491.50	$491.40