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	$81.80	12.245%	$91.8164	$91.82	$91.80	$91.80
Purchase #2	$133.40	12.868%	$150.5659	$150.57	$150.55	$150.60
Purchase #3	$85.98	12.185%	$96.4567	$96.46	$96.45	$96.50
Purchase #4	$29.25	6.440%	$31.1337	$31.13	$31.15	$31.10
Purchase #5	$92.45	8.590%	$100.3915	$100.39	$100.40	$100.40
Purchase #6	$129.91	10.191%	$143.1491	$143.15	$143.15	$143.10
Purchase #7	$228.43	4.774%	$239.3352	$239.34	$239.35	$239.30
7 purchase totals =	$781.22		$852.8485	$852.86	$852.85	$852.80