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	$120.34	9.208%	$131.4209	$131.42	$131.40	$131.40
Purchase #2	$109.25	4.226%	$113.8669	$113.87	$113.85	$113.90
Purchase #3	$159.58	6.336%	$169.691	$169.69	$169.70	$169.70
Purchase #4	$221.77	6.586%	$236.3758	$236.38	$236.40	$236.40
Purchase #5	$123.27	13.376%	$139.7586	$139.76	$139.75	$139.80
Purchase #6	$6.88	4.337%	$7.1784	$7.18	$7.20	$7.20
Purchase #7	$123.45	6.187%	$131.0879	$131.09	$131.10	$131.10
7 purchase totals =	$864.54		$929.3795	$929.39	$929.40	$929.50