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	$48.47	6.715%	$51.7248	$51.72	$51.70	$51.70
Purchase #2	$105.52	11.492%	$117.6464	$117.65	$117.65	$117.60
Purchase #3	$42.29	8.502%	$45.8855	$45.89	$45.90	$45.90
Purchase #4	$227.31	5.169%	$239.0597	$239.06	$239.05	$239.10
Purchase #5	$162.71	11.546%	$181.4965	$181.50	$181.50	$181.50
Purchase #6	$105.57	7.281%	$113.2566	$113.26	$113.25	$113.30
Purchase #7	$170.98	7.263%	$183.3983	$183.40	$183.40	$183.40
7 purchase totals =	$862.85		$932.4678	$932.48	$932.45	$932.50