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	$241.49	11.353%	$268.9064	$268.91	$268.90	$268.90
Purchase #2	$10.57	8.225%	$11.4394	$11.44	$11.45	$11.40
Purchase #3	$60.72	11.332%	$67.6008	$67.60	$67.60	$67.60
Purchase #4	$185.27	12.196%	$207.8655	$207.87	$207.85	$207.90
Purchase #5	$82.76	8.168%	$89.5198	$89.52	$89.50	$89.50
Purchase #6	$218.43	10.279%	$240.8824	$240.88	$240.90	$240.90
Purchase #7	$42.80	5.802%	$45.2833	$45.28	$45.30	$45.30
7 purchase totals =	$842.04		$931.4976	$931.50	$931.50	$931.50