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	$247.88	4.216%	$258.3306	$258.33	$258.35	$258.30
Purchase #2	$65.69	9.813%	$72.1362	$72.14	$72.15	$72.10
Purchase #3	$118.50	10.163%	$130.5432	$130.54	$130.55	$130.50
Purchase #4	$13.50	4.605%	$14.1217	$14.12	$14.10	$14.10
Purchase #5	$144.41	5.779%	$152.7555	$152.76	$152.75	$152.80
Purchase #6	$156.48	13.472%	$177.561	$177.56	$177.55	$177.60
Purchase #7	$73.61	12.500%	$82.8113	$82.81	$82.80	$82.80
7 purchase totals =	$820.07		$888.2595	$888.26	$888.25	$888.20