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	$44.69	7.152%	$47.8862	$47.89	$47.90	$47.90
Purchase #2	$65.89	9.720%	$72.2945	$72.29	$72.30	$72.30
Purchase #3	$40.27	4.843%	$42.2203	$42.22	$42.20	$42.20
Purchase #4	$195.36	7.649%	$210.3031	$210.30	$210.30	$210.30
Purchase #5	$35.42	11.171%	$39.3768	$39.38	$39.40	$39.40
Purchase #6	$222.74	8.852%	$242.4569	$242.46	$242.45	$242.50
Purchase #7	$165.87	3.450%	$171.5925	$171.59	$171.60	$171.60
7 purchase totals =	$770.24		$826.1303	$826.13	$826.15	$826.20