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	$240.40	6.390%	$255.7616	$255.76	$255.75	$255.80
Purchase #2	$196.36	10.426%	$216.8325	$216.83	$216.85	$216.80
Purchase #3	$19.64	6.389%	$20.8948	$20.89	$20.90	$20.90
Purchase #4	$214.96	9.391%	$235.1469	$235.15	$235.15	$235.10
Purchase #5	$63.74	12.633%	$71.7923	$71.79	$71.80	$71.80
Purchase #6	$104.63	8.164%	$113.172	$113.17	$113.15	$113.20
Purchase #7	$15.33	4.110%	$15.9601	$15.96	$15.95	$16.00
7 purchase totals =	$855.06		$929.5602	$929.55	$929.55	$929.60