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	$19.40	6.820%	$20.7231	$20.72	$20.70	$20.70
Purchase #2	$174.82	13.599%	$198.5938	$198.59	$198.60	$198.60
Purchase #3	$238.70	4.407%	$249.2195	$249.22	$249.20	$249.20
Purchase #4	$148.81	5.784%	$157.4172	$157.42	$157.40	$157.40
Purchase #5	$75.71	3.740%	$78.5416	$78.54	$78.55	$78.50
Purchase #6	$70.78	8.220%	$76.5981	$76.60	$76.60	$76.60
Purchase #7	$245.47	8.660%	$266.7277	$266.73	$266.75	$266.70
7 purchase totals =	$973.69		$1,047.8210	$1,047.82	$1,047.80	$1,047.70