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	$74.33	9.104%	$81.097	$81.10	$81.10	$81.10
Purchase #2	$249.71	11.690%	$278.9011	$278.90	$278.90	$278.90
Purchase #3	$138.48	8.722%	$150.5582	$150.56	$150.55	$150.60
Purchase #4	$248.61	3.572%	$257.4903	$257.49	$257.50	$257.50
Purchase #5	$96.49	13.260%	$109.2846	$109.28	$109.30	$109.30
Purchase #6	$108.85	13.618%	$123.6732	$123.67	$123.65	$123.70
Purchase #7	$86.44	13.776%	$98.348	$98.35	$98.35	$98.30
7 purchase totals =	$1,002.91		$1,099.3524	$1,099.35	$1,099.35	$1,099.40