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	$85.79	5.824%	$90.7864	$90.79	$90.80	$90.80
Purchase #2	$131.53	5.553%	$138.8339	$138.83	$138.85	$138.80
Purchase #3	$130.28	9.677%	$142.8872	$142.89	$142.90	$142.90
Purchase #4	$211.60	5.695%	$223.6506	$223.65	$223.65	$223.70
Purchase #5	$22.60	11.756%	$25.2569	$25.26	$25.25	$25.30
Purchase #6	$64.85	4.494%	$67.7644	$67.76	$67.75	$67.80
Purchase #7	$123.54	5.359%	$130.1605	$130.16	$130.15	$130.20
7 purchase totals =	$770.19		$819.3399	$819.34	$819.35	$819.50