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	$91.57	8.121%	$99.0064	$99.01	$99.00	$99.00
Purchase #2	$107.61	4.259%	$112.1931	$112.19	$112.20	$112.20
Purchase #3	$134.85	5.731%	$142.5783	$142.58	$142.60	$142.60
Purchase #4	$248.27	4.478%	$259.3875	$259.39	$259.40	$259.40
Purchase #5	$227.35	10.368%	$250.9216	$250.92	$250.90	$250.90
Purchase #6	$75.86	4.817%	$79.5142	$79.51	$79.50	$79.50
Purchase #7	$244.73	8.602%	$265.7817	$265.78	$265.80	$265.80
7 purchase totals =	$1,130.24		$1,209.3828	$1,209.38	$1,209.40	$1,209.40