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	$95.45	7.238%	$102.3587	$102.36	$102.35	$102.40
Purchase #2	$119.33	6.245%	$126.7822	$126.78	$126.80	$126.80
Purchase #3	$106.45	12.117%	$119.3485	$119.35	$119.35	$119.30
Purchase #4	$52.91	12.855%	$59.7116	$59.71	$59.70	$59.70
Purchase #5	$53.58	11.168%	$59.5638	$59.56	$59.55	$59.60
Purchase #6	$80.29	10.680%	$88.865	$88.87	$88.85	$88.90
Purchase #7	$33.28	3.118%	$34.3177	$34.32	$34.30	$34.30
7 purchase totals =	$541.29		$590.9475	$590.95	$590.90	$591.00