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	$36.73	13.712%	$41.7664	$41.77	$41.75	$41.80
Purchase #2	$139.94	8.241%	$151.4725	$151.47	$151.45	$151.50
Purchase #3	$102.28	4.497%	$106.8795	$106.88	$106.90	$106.90
Purchase #4	$214.85	6.830%	$229.5243	$229.52	$229.50	$229.50
Purchase #5	$165.32	8.168%	$178.8233	$178.82	$178.80	$178.80
Purchase #6	$47.78	5.537%	$50.4256	$50.43	$50.45	$50.40
Purchase #7	$77.68	12.423%	$87.3302	$87.33	$87.35	$87.30
7 purchase totals =	$784.58		$846.2218	$846.22	$846.20	$846.20