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	$46.38	8.220%	$50.1924	$50.19	$50.20	$50.20
Purchase #2	$9.64	3.812%	$10.0075	$10.01	$10.00	$10.00
Purchase #3	$105.40	3.853%	$109.4611	$109.46	$109.45	$109.50
Purchase #4	$92.47	4.173%	$96.3288	$96.33	$96.35	$96.30
Purchase #5	$57.89	10.776%	$64.1282	$64.13	$64.15	$64.10
Purchase #6	$41.72	10.418%	$46.0664	$46.07	$46.05	$46.10
Purchase #7	$137.37	11.132%	$152.662	$152.66	$152.65	$152.70
7 purchase totals =	$490.87		$528.8464	$528.85	$528.85	$528.90