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	$22.71	6.712%	$24.2343	$24.23	$24.25	$24.20
Purchase #2	$58.35	4.422%	$60.9302	$60.93	$60.95	$60.90
Purchase #3	$189.36	8.184%	$204.8572	$204.86	$204.85	$204.90
Purchase #4	$180.80	8.798%	$196.7068	$196.71	$196.70	$196.70
Purchase #5	$63.85	3.422%	$66.0349	$66.03	$66.05	$66.00
Purchase #6	$52.90	12.222%	$59.3654	$59.37	$59.35	$59.40
Purchase #7	$44.66	4.837%	$46.8202	$46.82	$46.80	$46.80
7 purchase totals =	$612.63		$658.9490	$658.95	$658.95	$658.90