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	$8.38	11.435%	$9.3383	$9.34	$9.35	$9.30
Purchase #2	$101.59	7.830%	$109.5445	$109.54	$109.55	$109.50
Purchase #3	$40.41	7.587%	$43.4759	$43.48	$43.50	$43.50
Purchase #4	$112.35	5.437%	$118.4585	$118.46	$118.45	$118.50
Purchase #5	$157.61	13.357%	$178.662	$178.66	$178.65	$178.70
Purchase #6	$45.25	6.544%	$48.2112	$48.21	$48.20	$48.20
Purchase #7	$149.77	6.599%	$159.6533	$159.65	$159.65	$159.70
7 purchase totals =	$615.36		$667.3437	$667.34	$667.35	$667.40