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	$136.70	6.265%	$145.2643	$145.26	$145.25	$145.30
Purchase #2	$83.69	11.845%	$93.6031	$93.60	$93.60	$93.60
Purchase #3	$82.29	10.482%	$90.9156	$90.92	$90.90	$90.90
Purchase #4	$30.85	6.224%	$32.7701	$32.77	$32.75	$32.80
Purchase #5	$41.33	4.176%	$43.0559	$43.06	$43.05	$43.10
Purchase #6	$163.59	10.313%	$180.461	$180.46	$180.45	$180.50
Purchase #7	$17.42	8.744%	$18.9432	$18.94	$18.95	$18.90
7 purchase totals =	$555.87		$605.0132	$605.01	$604.95	$605.10