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	$94.36	9.859%	$103.663	$103.66	$103.65	$103.70
Purchase #2	$232.30	9.575%	$254.5427	$254.54	$254.55	$254.50
Purchase #3	$88.52	5.162%	$93.0894	$93.09	$93.10	$93.10
Purchase #4	$244.88	11.433%	$272.8771	$272.88	$272.90	$272.90
Purchase #5	$53.59	12.435%	$60.2539	$60.25	$60.25	$60.30
Purchase #6	$24.85	10.653%	$27.4973	$27.50	$27.50	$27.50
Purchase #7	$165.81	13.299%	$187.8611	$187.86	$187.85	$187.90
7 purchase totals =	$904.31		$999.7845	$999.78	$999.80	$999.90