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	$221.39	8.556%	$240.3321	$240.33	$240.35	$240.30
Purchase #2	$131.66	8.711%	$143.1289	$143.13	$143.15	$143.10
Purchase #3	$119.28	6.729%	$127.3064	$127.31	$127.30	$127.30
Purchase #4	$43.55	3.764%	$45.1892	$45.19	$45.20	$45.20
Purchase #5	$184.78	5.686%	$195.2866	$195.29	$195.30	$195.30
Purchase #6	$132.58	3.828%	$137.6552	$137.66	$137.65	$137.70
Purchase #7	$57.46	12.235%	$64.4902	$64.49	$64.50	$64.50
7 purchase totals =	$890.70		$953.3886	$953.40	$953.45	$953.40