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	$142.63	12.126%	$159.9253	$159.93	$159.95	$159.90
Purchase #2	$45.58	10.173%	$50.2169	$50.22	$50.20	$50.20
Purchase #3	$86.29	4.742%	$90.3819	$90.38	$90.40	$90.40
Purchase #4	$36.30	4.871%	$38.0682	$38.07	$38.05	$38.10
Purchase #5	$230.26	6.527%	$245.2891	$245.29	$245.30	$245.30
Purchase #6	$49.86	10.459%	$55.0749	$55.07	$55.05	$55.10
Purchase #7	$207.80	4.209%	$216.5463	$216.55	$216.55	$216.50
7 purchase totals =	$798.72		$855.5026	$855.51	$855.50	$855.50