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	$37.42	13.468%	$42.4597	$42.46	$42.45	$42.50
Purchase #2	$142.49	6.584%	$151.8715	$151.87	$151.85	$151.90
Purchase #3	$64.99	11.808%	$72.664	$72.66	$72.65	$72.70
Purchase #4	$194.42	11.110%	$216.0201	$216.02	$216.00	$216.00
Purchase #5	$194.88	12.709%	$219.6473	$219.65	$219.65	$219.60
Purchase #6	$14.35	13.261%	$16.253	$16.25	$16.25	$16.30
Purchase #7	$85.50	4.185%	$89.0782	$89.08	$89.10	$89.10
7 purchase totals =	$734.05		$807.9938	$807.99	$807.95	$808.10