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	$150.32	12.342%	$168.8725	$168.87	$168.85	$168.90
Purchase #2	$49.72	10.858%	$55.1186	$55.12	$55.10	$55.10
Purchase #3	$193.32	3.370%	$199.8349	$199.83	$199.85	$199.80
Purchase #4	$25.41	8.416%	$27.5485	$27.55	$27.55	$27.50
Purchase #5	$10.96	5.446%	$11.5569	$11.56	$11.55	$11.60
Purchase #6	$96.63	13.411%	$109.589	$109.59	$109.60	$109.60
Purchase #7	$163.37	7.850%	$176.1945	$176.19	$176.20	$176.20
7 purchase totals =	$689.73		$748.7149	$748.71	$748.70	$748.70