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	$218.50	11.321%	$243.2364	$243.24	$243.25	$243.20
Purchase #2	$129.74	9.172%	$141.6398	$141.64	$141.65	$141.60
Purchase #3	$27.90	5.682%	$29.4853	$29.49	$29.50	$29.50
Purchase #4	$28.60	4.522%	$29.8933	$29.89	$29.90	$29.90
Purchase #5	$53.91	9.669%	$59.1226	$59.12	$59.10	$59.10
Purchase #6	$232.42	12.347%	$261.1169	$261.12	$261.10	$261.10
Purchase #7	$89.42	6.547%	$95.2743	$95.27	$95.25	$95.30
7 purchase totals =	$780.49		$859.7686	$859.77	$859.75	$859.70