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	$59.66	8.541%	$64.7556	$64.76	$64.75	$64.80
Purchase #2	$123.83	4.245%	$129.0866	$129.09	$129.10	$129.10
Purchase #3	$29.60	13.629%	$33.6342	$33.63	$33.65	$33.60
Purchase #4	$100.38	5.488%	$105.8889	$105.89	$105.90	$105.90
Purchase #5	$88.29	12.157%	$99.0234	$99.02	$99.00	$99.00
Purchase #6	$227.77	13.490%	$258.4962	$258.50	$258.50	$258.50
Purchase #7	$139.27	3.112%	$143.6041	$143.60	$143.60	$143.60
7 purchase totals =	$768.80		$834.4890	$834.49	$834.50	$834.50