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	$26.96	5.294%	$28.3873	$28.39	$28.40	$28.40
Purchase #2	$115.27	9.544%	$126.2714	$126.27	$126.25	$126.30
Purchase #3	$57.41	5.586%	$60.6169	$60.62	$60.60	$60.60
Purchase #4	$85.30	4.400%	$89.0532	$89.05	$89.05	$89.10
Purchase #5	$36.37	4.301%	$37.9343	$37.93	$37.95	$37.90
Purchase #6	$115.50	6.624%	$123.1507	$123.15	$123.15	$123.20
Purchase #7	$221.57	5.553%	$233.8738	$233.87	$233.85	$233.90
7 purchase totals =	$658.38		$699.2876	$699.28	$699.25	$699.40