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	$7.76	9.678%	$8.511	$8.51	$8.50	$8.50
Purchase #2	$29.38	10.606%	$32.496	$32.50	$32.50	$32.50
Purchase #3	$55.74	3.225%	$57.5376	$57.54	$57.55	$57.50
Purchase #4	$162.25	4.728%	$169.9212	$169.92	$169.90	$169.90
Purchase #5	$240.50	12.713%	$271.0748	$271.07	$271.05	$271.10
Purchase #6	$18.62	11.739%	$20.8058	$20.81	$20.80	$20.80
Purchase #7	$137.52	6.747%	$146.7985	$146.80	$146.80	$146.80
7 purchase totals =	$651.77		$707.1449	$707.15	$707.10	$707.10