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	$181.58	6.670%	$193.6914	$193.69	$193.70	$193.70
Purchase #2	$189.59	8.591%	$205.8777	$205.88	$205.90	$205.90
Purchase #3	$177.25	10.774%	$196.3469	$196.35	$196.35	$196.30
Purchase #4	$103.47	5.650%	$109.3161	$109.32	$109.30	$109.30
Purchase #5	$84.27	12.520%	$94.8206	$94.82	$94.80	$94.80
Purchase #6	$61.39	10.530%	$67.8544	$67.85	$67.85	$67.90
Purchase #7	$11.92	7.270%	$12.7866	$12.79	$12.80	$12.80
7 purchase totals =	$809.47		$880.6937	$880.70	$880.70	$880.70