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	$57.90	13.230%	$65.5602	$65.56	$65.55	$65.60
Purchase #2	$33.64	6.628%	$35.8697	$35.87	$35.85	$35.90
Purchase #3	$111.77	9.844%	$122.7726	$122.77	$122.75	$122.80
Purchase #4	$133.38	7.136%	$142.898	$142.90	$142.90	$142.90
Purchase #5	$114.27	11.427%	$127.3276	$127.33	$127.35	$127.30
Purchase #6	$207.51	4.213%	$216.2524	$216.25	$216.25	$216.30
Purchase #7	$200.33	8.765%	$217.8889	$217.89	$217.90	$217.90
7 purchase totals =	$858.80		$928.5694	$928.57	$928.55	$928.70