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	$38.60	6.721%	$41.1943	$41.19	$41.20	$41.20
Purchase #2	$199.27	9.481%	$218.1628	$218.16	$218.15	$218.20
Purchase #3	$152.51	4.341%	$159.1305	$159.13	$159.15	$159.10
Purchase #4	$84.26	7.868%	$90.8896	$90.89	$90.90	$90.90
Purchase #5	$143.42	5.651%	$151.5247	$151.52	$151.50	$151.50
Purchase #6	$7.26	10.871%	$8.0492	$8.05	$8.05	$8.00
Purchase #7	$53.35	11.264%	$59.3593	$59.36	$59.35	$59.40
7 purchase totals =	$678.67		$728.3104	$728.30	$728.30	$728.30