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	$22.44	13.336%	$25.4326	$25.43	$25.45	$25.40
Purchase #2	$174.67	10.530%	$193.0628	$193.06	$193.05	$193.10
Purchase #3	$78.40	13.690%	$89.133	$89.13	$89.15	$89.10
Purchase #4	$80.41	11.438%	$89.6073	$89.61	$89.60	$89.60
Purchase #5	$86.51	13.223%	$97.9492	$97.95	$97.95	$97.90
Purchase #6	$229.83	5.485%	$242.4362	$242.44	$242.45	$242.40
Purchase #7	$79.39	4.167%	$82.6982	$82.70	$82.70	$82.70
7 purchase totals =	$751.65		$820.3193	$820.32	$820.35	$820.20