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	$12.96	10.583%	$14.3316	$14.33	$14.35	$14.30
Purchase #2	$123.31	9.425%	$134.932	$134.93	$134.95	$134.90
Purchase #3	$83.91	7.810%	$90.4634	$90.46	$90.45	$90.50
Purchase #4	$24.70	3.412%	$25.5428	$25.54	$25.55	$25.50
Purchase #5	$77.82	13.736%	$88.5094	$88.51	$88.50	$88.50
Purchase #6	$28.96	11.766%	$32.3674	$32.37	$32.35	$32.40
Purchase #7	$185.88	8.662%	$201.9809	$201.98	$202.00	$202.00
7 purchase totals =	$537.54		$588.1275	$588.12	$588.15	$588.10