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	$34.65	6.863%	$37.028	$37.03	$37.05	$37.00
Purchase #2	$168.26	9.760%	$184.6822	$184.68	$184.70	$184.70
Purchase #3	$62.32	8.248%	$67.4602	$67.46	$67.45	$67.50
Purchase #4	$38.64	4.275%	$40.2919	$40.29	$40.30	$40.30
Purchase #5	$187.45	6.415%	$199.4749	$199.47	$199.45	$199.50
Purchase #6	$243.32	12.600%	$273.9783	$273.98	$274.00	$274.00
Purchase #7	$92.53	3.829%	$96.073	$96.07	$96.05	$96.10
7 purchase totals =	$827.17		$898.9885	$898.98	$899.00	$899.10