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	$52.55	5.129%	$55.2453	$55.25	$55.25	$55.20
Purchase #2	$184.80	3.802%	$191.8261	$191.83	$191.85	$191.80
Purchase #3	$98.33	13.328%	$111.4354	$111.44	$111.45	$111.40
Purchase #4	$190.26	11.764%	$212.6422	$212.64	$212.65	$212.60
Purchase #5	$134.51	8.514%	$145.9622	$145.96	$145.95	$146.00
Purchase #6	$36.89	7.787%	$39.7626	$39.76	$39.75	$39.80
Purchase #7	$220.29	12.545%	$247.9254	$247.93	$247.95	$247.90
7 purchase totals =	$917.63		$1,004.7992	$1,004.81	$1,004.85	$1,004.70