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	$205.78	3.673%	$213.3383	$213.34	$213.35	$213.30
Purchase #2	$120.43	13.125%	$136.2364	$136.24	$136.25	$136.20
Purchase #3	$176.96	12.811%	$199.6303	$199.63	$199.65	$199.60
Purchase #4	$28.68	9.819%	$31.4961	$31.50	$31.50	$31.50
Purchase #5	$138.91	8.220%	$150.3284	$150.33	$150.35	$150.30
Purchase #6	$20.40	6.762%	$21.7794	$21.78	$21.80	$21.80
Purchase #7	$79.53	13.776%	$90.4861	$90.49	$90.50	$90.50
7 purchase totals =	$770.69		$843.2950	$843.31	$843.40	$843.20