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	$139.75	4.685%	$146.2973	$146.30	$146.30	$146.30
Purchase #2	$157.87	10.300%	$174.1306	$174.13	$174.15	$174.10
Purchase #3	$215.54	13.769%	$245.2177	$245.22	$245.20	$245.20
Purchase #4	$182.71	7.723%	$196.8207	$196.82	$196.80	$196.80
Purchase #5	$153.78	9.315%	$168.1046	$168.10	$168.10	$168.10
Purchase #6	$226.85	5.660%	$239.6897	$239.69	$239.70	$239.70
Purchase #7	$100.30	10.776%	$111.1083	$111.11	$111.10	$111.10
7 purchase totals =	$1,176.80		$1,281.3689	$1,281.37	$1,281.35	$1,281.30