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	$242.77	5.155%	$255.2848	$255.28	$255.30	$255.30
Purchase #2	$160.63	5.790%	$169.9305	$169.93	$169.95	$169.90
Purchase #3	$214.48	11.513%	$239.1731	$239.17	$239.15	$239.20
Purchase #4	$88.85	3.780%	$92.2085	$92.21	$92.20	$92.20
Purchase #5	$41.64	4.702%	$43.5979	$43.60	$43.60	$43.60
Purchase #6	$98.34	7.426%	$105.6427	$105.64	$105.65	$105.60
Purchase #7	$90.77	4.445%	$94.8047	$94.80	$94.80	$94.80
7 purchase totals =	$937.48		$1,000.6422	$1,000.63	$1,000.65	$1,000.60