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	$11.78	6.495%	$12.5451	$12.55	$12.55	$12.50
Purchase #2	$59.56	9.387%	$65.1509	$65.15	$65.15	$65.20
Purchase #3	$244.45	4.154%	$254.6045	$254.60	$254.60	$254.60
Purchase #4	$182.41	7.670%	$196.4008	$196.40	$196.40	$196.40
Purchase #5	$73.89	12.148%	$82.8662	$82.87	$82.85	$82.90
Purchase #6	$95.65	4.215%	$99.6816	$99.68	$99.70	$99.70
Purchase #7	$78.99	11.321%	$87.9325	$87.93	$87.95	$87.90
7 purchase totals =	$746.73		$799.1816	$799.18	$799.20	$799.20