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	$41.91	10.420%	$46.277	$46.28	$46.30	$46.30
Purchase #2	$233.79	11.196%	$259.9651	$259.97	$259.95	$260.00
Purchase #3	$100.83	4.504%	$105.3714	$105.37	$105.35	$105.40
Purchase #4	$41.89	10.870%	$46.4434	$46.44	$46.45	$46.40
Purchase #5	$219.33	11.296%	$244.1055	$244.11	$244.10	$244.10
Purchase #6	$36.64	10.471%	$40.4766	$40.48	$40.50	$40.50
Purchase #7	$142.50	3.246%	$147.1256	$147.13	$147.15	$147.10
7 purchase totals =	$816.89		$889.7646	$889.78	$889.80	$889.80