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	$120.90	5.840%	$127.9606	$127.96	$127.95	$128.00
Purchase #2	$120.97	5.226%	$127.2919	$127.29	$127.30	$127.30
Purchase #3	$222.73	6.698%	$237.6485	$237.65	$237.65	$237.60
Purchase #4	$107.44	4.650%	$112.436	$112.44	$112.45	$112.40
Purchase #5	$154.72	9.751%	$169.8067	$169.81	$169.80	$169.80
Purchase #6	$72.38	8.410%	$78.4672	$78.47	$78.45	$78.50
Purchase #7	$203.85	11.417%	$227.1236	$227.12	$227.10	$227.10
7 purchase totals =	$1,002.99		$1,080.7345	$1,080.74	$1,080.70	$1,080.70