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	$189.30	13.829%	$215.4783	$215.48	$215.50	$215.50
Purchase #2	$216.79	6.639%	$231.1827	$231.18	$231.20	$231.20
Purchase #3	$187.89	6.776%	$200.6214	$200.62	$200.60	$200.60
Purchase #4	$50.69	10.392%	$55.9577	$55.96	$55.95	$56.00
Purchase #5	$16.59	5.746%	$17.5433	$17.54	$17.55	$17.50
Purchase #6	$211.62	8.248%	$229.0744	$229.07	$229.05	$229.10
Purchase #7	$123.60	6.383%	$131.4894	$131.49	$131.50	$131.50
7 purchase totals =	$996.48		$1,081.3472	$1,081.34	$1,081.35	$1,081.40