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	$181.39	4.204%	$189.0156	$189.02	$189.00	$189.00
Purchase #2	$33.83	4.679%	$35.4129	$35.41	$35.40	$35.40
Purchase #3	$63.64	3.764%	$66.0354	$66.04	$66.05	$66.00
Purchase #4	$180.55	4.804%	$189.2236	$189.22	$189.20	$189.20
Purchase #5	$241.81	9.842%	$265.6089	$265.61	$265.60	$265.60
Purchase #6	$219.67	3.505%	$227.3694	$227.37	$227.35	$227.40
Purchase #7	$114.27	7.666%	$123.0299	$123.03	$123.05	$123.00
7 purchase totals =	$1,035.16		$1,095.6957	$1,095.70	$1,095.65	$1,095.60