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	$8.59	5.171%	$9.0342	$9.03	$9.05	$9.00
Purchase #2	$220.86	12.785%	$249.097	$249.10	$249.10	$249.10
Purchase #3	$42.71	7.472%	$45.9013	$45.90	$45.90	$45.90
Purchase #4	$184.53	3.215%	$190.4626	$190.46	$190.45	$190.50
Purchase #5	$117.46	8.378%	$127.3008	$127.30	$127.30	$127.30
Purchase #6	$193.53	9.794%	$212.4843	$212.48	$212.50	$212.50
Purchase #7	$16.76	10.453%	$18.5119	$18.51	$18.50	$18.50
7 purchase totals =	$784.44		$852.7921	$852.78	$852.80	$852.80