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	$82.67	5.869%	$87.5219	$87.52	$87.50	$87.50
Purchase #2	$161.75	6.608%	$172.4384	$172.44	$172.45	$172.40
Purchase #3	$12.64	9.871%	$13.8877	$13.89	$13.90	$13.90
Purchase #4	$121.55	7.650%	$130.8486	$130.85	$130.85	$130.80
Purchase #5	$188.83	8.846%	$205.5339	$205.53	$205.55	$205.50
Purchase #6	$59.30	13.591%	$67.3595	$67.36	$67.35	$67.40
Purchase #7	$195.33	13.505%	$221.7093	$221.71	$221.70	$221.70
7 purchase totals =	$822.07		$899.2993	$899.30	$899.30	$899.20