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	$82.88	7.794%	$89.3397	$89.34	$89.35	$89.30
Purchase #2	$81.44	3.248%	$84.0852	$84.09	$84.10	$84.10
Purchase #3	$13.56	6.852%	$14.4891	$14.49	$14.50	$14.50
Purchase #4	$102.50	7.150%	$109.8288	$109.83	$109.85	$109.80
Purchase #5	$100.53	4.754%	$105.3092	$105.31	$105.30	$105.30
Purchase #6	$31.73	8.757%	$34.5086	$34.51	$34.50	$34.50
Purchase #7	$177.68	11.168%	$197.5233	$197.52	$197.50	$197.50
7 purchase totals =	$590.32		$635.0839	$635.09	$635.10	$635.00