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	$98.77	6.144%	$104.8384	$104.84	$104.85	$104.80
Purchase #2	$97.31	9.454%	$106.5097	$106.51	$106.50	$106.50
Purchase #3	$234.40	10.674%	$259.4199	$259.42	$259.40	$259.40
Purchase #4	$18.91	8.503%	$20.5179	$20.52	$20.50	$20.50
Purchase #5	$133.83	8.242%	$144.8603	$144.86	$144.85	$144.90
Purchase #6	$97.33	8.320%	$105.4279	$105.43	$105.45	$105.40
Purchase #7	$14.49	12.165%	$16.2527	$16.25	$16.25	$16.30
7 purchase totals =	$695.04		$757.8268	$757.83	$757.80	$757.80