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	$145.32	3.294%	$150.1068	$150.11	$150.10	$150.10
Purchase #2	$199.26	11.681%	$222.5356	$222.54	$222.55	$222.50
Purchase #3	$132.61	13.425%	$150.4129	$150.41	$150.40	$150.40
Purchase #4	$137.51	4.187%	$143.2675	$143.27	$143.25	$143.30
Purchase #5	$150.68	5.684%	$159.2447	$159.24	$159.25	$159.20
Purchase #6	$236.94	3.368%	$244.9201	$244.92	$244.90	$244.90
Purchase #7	$15.68	4.796%	$16.432	$16.43	$16.45	$16.40
7 purchase totals =	$1,018.00		$1,086.9196	$1,086.92	$1,086.90	$1,086.80