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	$37.45	7.772%	$40.3606	$40.36	$40.35	$40.40
Purchase #2	$53.38	12.211%	$59.8982	$59.90	$59.90	$59.90
Purchase #3	$222.30	8.217%	$240.5664	$240.57	$240.55	$240.60
Purchase #4	$143.58	6.476%	$152.8782	$152.88	$152.90	$152.90
Purchase #5	$116.45	12.157%	$130.6068	$130.61	$130.60	$130.60
Purchase #6	$166.52	10.417%	$183.8664	$183.87	$183.85	$183.90
Purchase #7	$18.58	7.856%	$20.0396	$20.04	$20.05	$20.00
7 purchase totals =	$758.26		$828.2162	$828.23	$828.20	$828.30