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	$27.90	10.346%	$30.7865	$30.79	$30.80	$30.80
Purchase #2	$209.25	3.725%	$217.0446	$217.04	$217.05	$217.00
Purchase #3	$10.32	11.843%	$11.5422	$11.54	$11.55	$11.50
Purchase #4	$79.35	13.113%	$89.7552	$89.76	$89.75	$89.80
Purchase #5	$127.93	10.470%	$141.3243	$141.32	$141.30	$141.30
Purchase #6	$162.56	6.678%	$173.4158	$173.42	$173.40	$173.40
Purchase #7	$193.49	11.812%	$216.345	$216.35	$216.35	$216.30
7 purchase totals =	$810.80		$880.2136	$880.22	$880.20	$880.10