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	$83.56	12.360%	$93.888	$93.89	$93.90	$93.90
Purchase #2	$234.46	5.416%	$247.1584	$247.16	$247.15	$247.20
Purchase #3	$57.26	11.647%	$63.9291	$63.93	$63.95	$63.90
Purchase #4	$95.34	10.187%	$105.0523	$105.05	$105.05	$105.10
Purchase #5	$185.96	10.320%	$205.1511	$205.15	$205.15	$205.20
Purchase #6	$205.29	7.806%	$221.3149	$221.31	$221.30	$221.30
Purchase #7	$118.78	3.636%	$123.0988	$123.10	$123.10	$123.10
7 purchase totals =	$980.65		$1,059.5926	$1,059.59	$1,059.60	$1,059.70