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	$139.33	11.531%	$155.3961	$155.40	$155.40	$155.40
Purchase #2	$102.52	9.402%	$112.1589	$112.16	$112.15	$112.20
Purchase #3	$105.61	7.289%	$113.3079	$113.31	$113.30	$113.30
Purchase #4	$31.81	3.503%	$32.9243	$32.92	$32.90	$32.90
Purchase #5	$96.60	3.531%	$100.0109	$100.01	$100.00	$100.00
Purchase #6	$81.51	11.494%	$90.8788	$90.88	$90.90	$90.90
Purchase #7	$75.42	9.363%	$82.4816	$82.48	$82.50	$82.50
7 purchase totals =	$632.80		$687.1585	$687.16	$687.15	$687.20