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	$10.75	9.723%	$11.7952	$11.80	$11.80	$11.80
Purchase #2	$75.42	13.531%	$85.6251	$85.63	$85.65	$85.60
Purchase #3	$180.31	4.776%	$188.9216	$188.92	$188.90	$188.90
Purchase #4	$40.65	6.460%	$43.276	$43.28	$43.30	$43.30
Purchase #5	$168.38	8.850%	$183.2816	$183.28	$183.30	$183.30
Purchase #6	$61.64	8.322%	$66.7697	$66.77	$66.75	$66.80
Purchase #7	$79.97	7.136%	$85.6767	$85.68	$85.70	$85.70
7 purchase totals =	$617.12		$665.3459	$665.36	$665.40	$665.40