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	$83.42	8.200%	$90.2604	$90.26	$90.25	$90.30
Purchase #2	$76.36	7.744%	$82.2733	$82.27	$82.25	$82.30
Purchase #3	$104.30	4.775%	$109.2803	$109.28	$109.30	$109.30
Purchase #4	$67.70	3.549%	$70.1027	$70.10	$70.10	$70.10
Purchase #5	$101.83	4.578%	$106.4918	$106.49	$106.50	$106.50
Purchase #6	$65.94	5.455%	$69.537	$69.54	$69.55	$69.50
Purchase #7	$122.83	12.667%	$138.3889	$138.39	$138.40	$138.40
7 purchase totals =	$622.38		$666.3344	$666.33	$666.35	$666.40