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	$226.45	8.860%	$246.5135	$246.51	$246.50	$246.50
Purchase #2	$34.36	13.199%	$38.8952	$38.90	$38.90	$38.90
Purchase #3	$139.76	4.306%	$145.7781	$145.78	$145.80	$145.80
Purchase #4	$168.60	5.196%	$177.3605	$177.36	$177.35	$177.40
Purchase #5	$29.49	13.584%	$33.4959	$33.50	$33.50	$33.50
Purchase #6	$38.66	10.278%	$42.6335	$42.63	$42.65	$42.60
Purchase #7	$178.87	6.682%	$190.8221	$190.82	$190.80	$190.80
7 purchase totals =	$816.19		$875.4988	$875.50	$875.50	$875.50