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	$183.89	12.153%	$206.2382	$206.24	$206.25	$206.20
Purchase #2	$37.91	13.186%	$42.9088	$42.91	$42.90	$42.90
Purchase #3	$131.90	5.681%	$139.3932	$139.39	$139.40	$139.40
Purchase #4	$244.72	6.126%	$259.7115	$259.71	$259.70	$259.70
Purchase #5	$130.43	11.819%	$145.8455	$145.85	$145.85	$145.80
Purchase #6	$88.87	4.385%	$92.7669	$92.77	$92.75	$92.80
Purchase #7	$155.53	12.467%	$174.9199	$174.92	$174.90	$174.90
7 purchase totals =	$973.25		$1,061.7840	$1,061.79	$1,061.75	$1,061.70