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	$49.28	6.434%	$52.4507	$52.45	$52.45	$52.50
Purchase #2	$91.63	9.303%	$100.1543	$100.15	$100.15	$100.20
Purchase #3	$145.93	11.243%	$162.3369	$162.34	$162.35	$162.30
Purchase #4	$40.79	11.550%	$45.5012	$45.50	$45.50	$45.50
Purchase #5	$186.35	4.732%	$195.1681	$195.17	$195.15	$195.20
Purchase #6	$157.61	11.266%	$175.3663	$175.37	$175.35	$175.40
Purchase #7	$51.50	10.424%	$56.8684	$56.87	$56.85	$56.90
7 purchase totals =	$723.09		$787.8459	$787.85	$787.80	$788.00