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	$19.59	4.515%	$20.4745	$20.47	$20.45	$20.50
Purchase #2	$131.27	12.764%	$148.0253	$148.03	$148.05	$148.00
Purchase #3	$100.61	13.701%	$114.3946	$114.39	$114.40	$114.40
Purchase #4	$134.39	8.254%	$145.4826	$145.48	$145.50	$145.50
Purchase #5	$118.62	6.502%	$126.3327	$126.33	$126.35	$126.30
Purchase #6	$196.65	12.699%	$221.6226	$221.62	$221.60	$221.60
Purchase #7	$95.46	3.498%	$98.7992	$98.80	$98.80	$98.80
7 purchase totals =	$796.59		$875.1315	$875.12	$875.15	$875.10