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	$53.60	10.154%	$59.0425	$59.04	$59.05	$59.00
Purchase #2	$69.69	13.615%	$79.1783	$79.18	$79.20	$79.20
Purchase #3	$141.88	13.108%	$160.4776	$160.48	$160.50	$160.50
Purchase #4	$94.92	5.466%	$100.1083	$100.11	$100.10	$100.10
Purchase #5	$192.87	11.397%	$214.8514	$214.85	$214.85	$214.90
Purchase #6	$51.78	13.407%	$58.7221	$58.72	$58.70	$58.70
Purchase #7	$6.65	7.129%	$7.1241	$7.12	$7.10	$7.10
7 purchase totals =	$611.39		$679.5043	$679.50	$679.50	$679.50