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	$67.50	5.242%	$71.0384	$71.04	$71.05	$71.00
Purchase #2	$122.79	12.239%	$137.8183	$137.82	$137.80	$137.80
Purchase #3	$124.47	12.424%	$139.9342	$139.93	$139.95	$139.90
Purchase #4	$190.45	10.520%	$210.4853	$210.49	$210.50	$210.50
Purchase #5	$43.95	13.540%	$49.9008	$49.90	$49.90	$49.90
Purchase #6	$131.76	6.549%	$140.389	$140.39	$140.40	$140.40
Purchase #7	$51.37	8.496%	$55.7344	$55.73	$55.75	$55.70
7 purchase totals =	$732.29		$805.3004	$805.30	$805.35	$805.20