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	$23.43	12.134%	$26.273	$26.27	$26.25	$26.30
Purchase #2	$183.45	7.308%	$196.8565	$196.86	$196.85	$196.90
Purchase #3	$140.75	13.635%	$159.9413	$159.94	$159.95	$159.90
Purchase #4	$122.82	9.416%	$134.3847	$134.38	$134.40	$134.40
Purchase #5	$94.92	4.104%	$98.8155	$98.82	$98.80	$98.80
Purchase #6	$58.85	13.414%	$66.7441	$66.74	$66.75	$66.70
Purchase #7	$165.51	3.627%	$171.513	$171.51	$171.50	$171.50
7 purchase totals =	$789.73		$854.5281	$854.52	$854.50	$854.50