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	$54.63	8.710%	$59.3883	$59.39	$59.40	$59.40
Purchase #2	$34.46	8.316%	$37.3257	$37.33	$37.35	$37.30
Purchase #3	$126.55	10.519%	$139.8618	$139.86	$139.85	$139.90
Purchase #4	$161.89	8.651%	$175.8951	$175.90	$175.90	$175.90
Purchase #5	$179.78	6.112%	$190.7682	$190.77	$190.75	$190.80
Purchase #6	$71.32	9.281%	$77.9392	$77.94	$77.95	$77.90
Purchase #7	$134.66	5.185%	$141.6421	$141.64	$141.65	$141.60
7 purchase totals =	$763.29		$822.8204	$822.83	$822.85	$822.80