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	$27.36	7.817%	$29.4987	$29.50	$29.50	$29.50
Purchase #2	$248.42	6.217%	$263.8643	$263.86	$263.85	$263.90
Purchase #3	$180.82	3.362%	$186.8992	$186.90	$186.90	$186.90
Purchase #4	$224.58	9.242%	$245.3357	$245.34	$245.35	$245.30
Purchase #5	$125.43	13.722%	$142.6415	$142.64	$142.65	$142.60
Purchase #6	$165.75	4.284%	$172.8507	$172.85	$172.85	$172.90
Purchase #7	$66.29	7.182%	$71.0509	$71.05	$71.05	$71.10
7 purchase totals =	$1,038.65		$1,112.1410	$1,112.14	$1,112.15	$1,112.20