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	$36.36	9.617%	$39.8567	$39.86	$39.85	$39.90
Purchase #2	$209.67	12.865%	$236.644	$236.64	$236.65	$236.60
Purchase #3	$64.80	3.536%	$67.0913	$67.09	$67.10	$67.10
Purchase #4	$130.78	8.640%	$142.0794	$142.08	$142.10	$142.10
Purchase #5	$131.93	11.139%	$146.6257	$146.63	$146.65	$146.60
Purchase #6	$71.32	8.566%	$77.4293	$77.43	$77.45	$77.40
Purchase #7	$40.45	12.567%	$45.5334	$45.53	$45.55	$45.50
7 purchase totals =	$685.31		$755.2598	$755.26	$755.35	$755.20