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	$215.29	5.797%	$227.7704	$227.77	$227.75	$227.80
Purchase #2	$78.65	9.118%	$85.8213	$85.82	$85.80	$85.80
Purchase #3	$137.66	7.780%	$148.3699	$148.37	$148.35	$148.40
Purchase #4	$35.73	4.504%	$37.3393	$37.34	$37.35	$37.30
Purchase #5	$16.43	12.602%	$18.5005	$18.50	$18.50	$18.50
Purchase #6	$165.38	10.725%	$183.117	$183.12	$183.10	$183.10
Purchase #7	$214.98	11.699%	$240.1305	$240.13	$240.15	$240.10
7 purchase totals =	$864.12		$941.0489	$941.05	$941.00	$941.00