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	$131.64	4.874%	$138.0561	$138.06	$138.05	$138.10
Purchase #2	$99.91	11.245%	$111.1449	$111.14	$111.15	$111.10
Purchase #3	$230.61	13.210%	$261.0736	$261.07	$261.05	$261.10
Purchase #4	$214.53	7.785%	$231.2312	$231.23	$231.25	$231.20
Purchase #5	$146.27	4.642%	$153.0599	$153.06	$153.05	$153.10
Purchase #6	$147.88	12.207%	$165.9317	$165.93	$165.95	$165.90
Purchase #7	$122.55	4.646%	$128.2437	$128.24	$128.25	$128.20
7 purchase totals =	$1,093.39		$1,188.7411	$1,188.73	$1,188.75	$1,188.70