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	$123.41	11.215%	$137.2504	$137.25	$137.25	$137.30
Purchase #2	$157.77	3.392%	$163.1216	$163.12	$163.10	$163.10
Purchase #3	$188.83	6.340%	$200.8018	$200.80	$200.80	$200.80
Purchase #4	$149.73	13.262%	$169.5872	$169.59	$169.60	$169.60
Purchase #5	$48.86	10.314%	$53.8994	$53.90	$53.90	$53.90
Purchase #6	$143.30	5.306%	$150.9035	$150.90	$150.90	$150.90
Purchase #7	$104.54	12.374%	$117.4758	$117.48	$117.50	$117.50
7 purchase totals =	$916.44		$993.0397	$993.04	$993.05	$993.10