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	$146.92	12.194%	$164.8354	$164.84	$164.85	$164.80
Purchase #2	$55.58	12.602%	$62.5842	$62.58	$62.60	$62.60
Purchase #3	$205.97	12.237%	$231.1745	$231.17	$231.15	$231.20
Purchase #4	$221.82	12.768%	$250.142	$250.14	$250.15	$250.10
Purchase #5	$182.41	12.533%	$205.2714	$205.27	$205.25	$205.30
Purchase #6	$152.38	11.254%	$169.5288	$169.53	$169.55	$169.50
Purchase #7	$131.43	4.730%	$137.6466	$137.65	$137.65	$137.60
7 purchase totals =	$1,096.51		$1,221.1829	$1,221.18	$1,221.20	$1,221.10