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	$147.62	6.243%	$156.8359	$156.84	$156.85	$156.80
Purchase #2	$148.73	9.155%	$162.3462	$162.35	$162.35	$162.30
Purchase #3	$107.86	4.308%	$112.5066	$112.51	$112.50	$112.50
Purchase #4	$66.84	8.773%	$72.7039	$72.70	$72.70	$72.70
Purchase #5	$222.40	9.394%	$243.2923	$243.29	$243.30	$243.30
Purchase #6	$90.97	9.404%	$99.5248	$99.52	$99.50	$99.50
Purchase #7	$38.27	9.694%	$41.9799	$41.98	$42.00	$42.00
7 purchase totals =	$822.69		$889.1896	$889.19	$889.20	$889.10