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	$134.29	4.637%	$140.517	$140.52	$140.50	$140.50
Purchase #2	$41.69	4.854%	$43.7136	$43.71	$43.70	$43.70
Purchase #3	$84.31	7.144%	$90.3331	$90.33	$90.35	$90.30
Purchase #4	$214.44	8.682%	$233.0577	$233.06	$233.05	$233.10
Purchase #5	$99.85	3.433%	$103.2779	$103.28	$103.30	$103.30
Purchase #6	$76.80	11.472%	$85.6105	$85.61	$85.60	$85.60
Purchase #7	$72.41	3.345%	$74.8321	$74.83	$74.85	$74.80
7 purchase totals =	$723.79		$771.3419	$771.34	$771.35	$771.30