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	$39.41	3.365%	$40.7361	$40.74	$40.75	$40.70
Purchase #2	$95.32	11.767%	$106.5363	$106.54	$106.55	$106.50
Purchase #3	$124.59	4.630%	$130.3585	$130.36	$130.35	$130.40
Purchase #4	$148.51	5.358%	$156.4672	$156.47	$156.45	$156.50
Purchase #5	$170.64	4.702%	$178.6635	$178.66	$178.65	$178.70
Purchase #6	$84.42	5.517%	$89.0775	$89.08	$89.10	$89.10
Purchase #7	$61.81	13.307%	$70.0351	$70.04	$70.05	$70.00
7 purchase totals =	$724.70		$771.8742	$771.89	$771.90	$771.90