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	$29.93	11.186%	$33.278	$33.28	$33.30	$33.30
Purchase #2	$109.38	13.868%	$124.5488	$124.55	$124.55	$124.50
Purchase #3	$249.91	13.423%	$283.4554	$283.46	$283.45	$283.50
Purchase #4	$125.69	10.850%	$139.3274	$139.33	$139.35	$139.30
Purchase #5	$169.99	7.346%	$182.4775	$182.48	$182.50	$182.50
Purchase #6	$82.41	10.297%	$90.8958	$90.90	$90.90	$90.90
Purchase #7	$135.30	6.640%	$144.2839	$144.28	$144.30	$144.30
7 purchase totals =	$902.61		$998.2668	$998.28	$998.35	$998.30