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	$98.87	13.178%	$111.8991	$111.90	$111.90	$111.90
Purchase #2	$57.44	3.398%	$59.3918	$59.39	$59.40	$59.40
Purchase #3	$141.28	6.591%	$150.5918	$150.59	$150.60	$150.60
Purchase #4	$64.64	10.516%	$71.4375	$71.44	$71.45	$71.40
Purchase #5	$66.56	11.711%	$74.3548	$74.35	$74.35	$74.40
Purchase #6	$14.62	12.548%	$16.4545	$16.45	$16.45	$16.50
Purchase #7	$162.35	6.754%	$173.3151	$173.32	$173.30	$173.30
7 purchase totals =	$605.76		$657.4446	$657.44	$657.45	$657.50