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	$161.76	11.661%	$180.6228	$180.62	$180.60	$180.60
Purchase #2	$103.74	9.236%	$113.3214	$113.32	$113.30	$113.30
Purchase #3	$241.27	3.197%	$248.9834	$248.98	$249.00	$249.00
Purchase #4	$85.64	6.690%	$91.3693	$91.37	$91.35	$91.40
Purchase #5	$62.41	7.828%	$67.2955	$67.30	$67.30	$67.30
Purchase #6	$50.59	5.499%	$53.3719	$53.37	$53.35	$53.40
Purchase #7	$99.71	9.406%	$109.0887	$109.09	$109.10	$109.10
7 purchase totals =	$805.12		$864.0530	$864.05	$864.00	$864.10