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	$16.89	3.653%	$17.507	$17.51	$17.50	$17.50
Purchase #2	$151.69	11.819%	$169.6182	$169.62	$169.60	$169.60
Purchase #3	$93.33	10.296%	$102.9393	$102.94	$102.95	$102.90
Purchase #4	$83.45	7.329%	$89.5661	$89.57	$89.55	$89.60
Purchase #5	$119.34	6.353%	$126.9217	$126.92	$126.90	$126.90
Purchase #6	$193.46	11.798%	$216.2844	$216.28	$216.30	$216.30
Purchase #7	$173.85	4.300%	$181.3256	$181.33	$181.35	$181.30
7 purchase totals =	$832.01		$904.1623	$904.17	$904.15	$904.10