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	$63.29	4.494%	$66.1343	$66.13	$66.15	$66.10
Purchase #2	$92.40	13.589%	$104.9562	$104.96	$104.95	$105.00
Purchase #3	$56.25	6.402%	$59.8511	$59.85	$59.85	$59.90
Purchase #4	$148.34	12.355%	$166.6674	$166.67	$166.65	$166.70
Purchase #5	$144.25	11.501%	$160.8402	$160.84	$160.85	$160.80
Purchase #6	$105.99	3.669%	$109.8788	$109.88	$109.90	$109.90
Purchase #7	$233.72	8.777%	$254.2336	$254.23	$254.25	$254.20
7 purchase totals =	$844.24		$922.5616	$922.56	$922.60	$922.60