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	$37.49	6.756%	$40.0228	$40.02	$40.00	$40.00
Purchase #2	$225.27	10.298%	$248.4683	$248.47	$248.45	$248.50
Purchase #3	$169.92	6.189%	$180.4363	$180.44	$180.45	$180.40
Purchase #4	$195.54	6.352%	$207.9607	$207.96	$207.95	$208.00
Purchase #5	$225.26	13.531%	$255.7399	$255.74	$255.75	$255.70
Purchase #6	$89.89	9.764%	$98.6669	$98.67	$98.65	$98.70
Purchase #7	$72.56	10.553%	$80.2173	$80.22	$80.20	$80.20
7 purchase totals =	$1,015.93		$1,111.5122	$1,111.52	$1,111.45	$1,111.50