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	$178.94	3.716%	$185.5894	$185.59	$185.60	$185.60
Purchase #2	$76.41	7.121%	$81.8512	$81.85	$81.85	$81.90
Purchase #3	$90.85	13.776%	$103.3655	$103.37	$103.35	$103.40
Purchase #4	$133.88	13.667%	$152.1774	$152.18	$152.20	$152.20
Purchase #5	$82.44	8.853%	$89.7384	$89.74	$89.75	$89.70
Purchase #6	$90.35	6.264%	$96.0095	$96.01	$96.00	$96.00
Purchase #7	$135.26	5.753%	$143.0415	$143.04	$143.05	$143.00
7 purchase totals =	$788.13		$851.7729	$851.78	$851.80	$851.80