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	$159.62	12.378%	$179.3778	$179.38	$179.40	$179.40
Purchase #2	$30.53	8.302%	$33.0646	$33.06	$33.05	$33.10
Purchase #3	$103.89	9.508%	$113.7679	$113.77	$113.75	$113.80
Purchase #4	$33.33	11.806%	$37.2649	$37.26	$37.25	$37.30
Purchase #5	$242.61	4.804%	$254.265	$254.27	$254.25	$254.30
Purchase #6	$39.81	13.873%	$45.3328	$45.33	$45.35	$45.30
Purchase #7	$107.35	9.671%	$117.7318	$117.73	$117.75	$117.70
7 purchase totals =	$717.14		$780.8048	$780.80	$780.80	$780.90