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	$159.27	3.280%	$164.4941	$164.49	$164.50	$164.50
Purchase #2	$38.84	8.203%	$42.026	$42.03	$42.05	$42.00
Purchase #3	$61.94	5.851%	$65.5641	$65.56	$65.55	$65.60
Purchase #4	$67.74	4.651%	$70.8906	$70.89	$70.90	$70.90
Purchase #5	$228.34	10.751%	$252.8888	$252.89	$252.90	$252.90
Purchase #6	$53.82	13.766%	$61.2289	$61.23	$61.25	$61.20
Purchase #7	$61.57	6.462%	$65.5487	$65.55	$65.55	$65.50
7 purchase totals =	$671.52		$722.6412	$722.64	$722.70	$722.60