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	$168.53	11.224%	$187.4458	$187.45	$187.45	$187.40
Purchase #2	$92.43	13.561%	$104.9644	$104.96	$104.95	$105.00
Purchase #3	$133.27	11.804%	$149.0012	$149.00	$149.00	$149.00
Purchase #4	$154.26	11.748%	$172.3825	$172.38	$172.40	$172.40
Purchase #5	$231.64	3.562%	$239.891	$239.89	$239.90	$239.90
Purchase #6	$98.85	6.266%	$105.0439	$105.04	$105.05	$105.00
Purchase #7	$35.67	13.190%	$40.3749	$40.37	$40.35	$40.40
7 purchase totals =	$914.65		$999.1037	$999.09	$999.10	$999.10