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	$138.83	5.516%	$146.4879	$146.49	$146.50	$146.50
Purchase #2	$87.37	3.604%	$90.5188	$90.52	$90.50	$90.50
Purchase #3	$221.94	4.331%	$231.5522	$231.55	$231.55	$231.60
Purchase #4	$130.99	5.216%	$137.8224	$137.82	$137.80	$137.80
Purchase #5	$250.33	9.191%	$273.3378	$273.34	$273.35	$273.30
Purchase #6	$176.99	11.173%	$196.7651	$196.77	$196.75	$196.80
Purchase #7	$37.65	12.445%	$42.3355	$42.34	$42.35	$42.30
7 purchase totals =	$1,044.10		$1,118.8197	$1,118.83	$1,118.80	$1,118.80