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	$115.85	7.310%	$124.3186	$124.32	$124.30	$124.30
Purchase #2	$186.79	7.408%	$200.6274	$200.63	$200.65	$200.60
Purchase #3	$113.56	8.665%	$123.4	$123.40	$123.40	$123.40
Purchase #4	$140.44	5.682%	$148.4198	$148.42	$148.40	$148.40
Purchase #5	$64.71	4.189%	$67.4207	$67.42	$67.40	$67.40
Purchase #6	$142.63	7.805%	$153.7623	$153.76	$153.75	$153.80
Purchase #7	$156.94	5.352%	$165.3394	$165.34	$165.35	$165.30
7 purchase totals =	$920.92		$983.2882	$983.29	$983.25	$983.20