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	$102.79	6.265%	$109.2298	$109.23	$109.25	$109.20
Purchase #2	$59.41	3.464%	$61.468	$61.47	$61.45	$61.50
Purchase #3	$149.89	7.330%	$160.8769	$160.88	$160.90	$160.90
Purchase #4	$102.78	7.624%	$110.6159	$110.62	$110.60	$110.60
Purchase #5	$28.35	3.431%	$29.3227	$29.32	$29.30	$29.30
Purchase #6	$53.87	7.377%	$57.844	$57.84	$57.85	$57.80
Purchase #7	$62.65	11.457%	$69.8278	$69.83	$69.85	$69.80
7 purchase totals =	$559.74		$599.1851	$599.19	$599.20	$599.10