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	$9.35	9.737%	$10.2604	$10.26	$10.25	$10.30
Purchase #2	$234.57	6.735%	$250.3683	$250.37	$250.35	$250.40
Purchase #3	$10.47	7.695%	$11.2757	$11.28	$11.30	$11.30
Purchase #4	$185.58	5.765%	$196.2787	$196.28	$196.30	$196.30
Purchase #5	$241.87	9.494%	$264.8331	$264.83	$264.85	$264.80
Purchase #6	$12.65	12.454%	$14.2254	$14.23	$14.25	$14.20
Purchase #7	$30.53	7.312%	$32.7624	$32.76	$32.75	$32.80
7 purchase totals =	$725.02		$780.0040	$780.01	$780.05	$780.10