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	$120.27	13.385%	$136.3681	$136.37	$136.35	$136.40
Purchase #2	$167.83	10.709%	$185.8029	$185.80	$185.80	$185.80
Purchase #3	$141.34	6.154%	$150.0381	$150.04	$150.05	$150.00
Purchase #4	$102.70	5.182%	$108.0219	$108.02	$108.00	$108.00
Purchase #5	$61.52	6.465%	$65.4973	$65.50	$65.50	$65.50
Purchase #6	$42.32	11.201%	$47.0603	$47.06	$47.05	$47.10
Purchase #7	$201.52	4.511%	$210.6106	$210.61	$210.60	$210.60
7 purchase totals =	$837.50		$903.3992	$903.40	$903.35	$903.40