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	$40.75	4.272%	$42.4908	$42.49	$42.50	$42.50
Purchase #2	$54.66	4.414%	$57.0727	$57.07	$57.05	$57.10
Purchase #3	$210.60	6.128%	$223.5056	$223.51	$223.50	$223.50
Purchase #4	$164.48	10.282%	$181.3918	$181.39	$181.40	$181.40
Purchase #5	$52.40	5.306%	$55.1803	$55.18	$55.20	$55.20
Purchase #6	$131.59	11.545%	$146.7821	$146.78	$146.80	$146.80
Purchase #7	$211.51	5.837%	$223.8558	$223.86	$223.85	$223.90
7 purchase totals =	$865.99		$930.2791	$930.28	$930.30	$930.40