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	$227.32	12.266%	$255.2031	$255.20	$255.20	$255.20
Purchase #2	$155.40	4.832%	$162.9089	$162.91	$162.90	$162.90
Purchase #3	$221.39	10.321%	$244.2397	$244.24	$244.25	$244.20
Purchase #4	$161.54	13.404%	$183.1928	$183.19	$183.20	$183.20
Purchase #5	$39.43	4.430%	$41.1767	$41.18	$41.20	$41.20
Purchase #6	$118.92	3.454%	$123.0275	$123.03	$123.05	$123.00
Purchase #7	$20.69	3.347%	$21.3825	$21.38	$21.40	$21.40
7 purchase totals =	$944.69		$1,031.1312	$1,031.13	$1,031.20	$1,031.10