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	$43.59	3.512%	$45.1209	$45.12	$45.10	$45.10
Purchase #2	$18.87	13.624%	$21.4408	$21.44	$21.45	$21.40
Purchase #3	$123.32	12.629%	$138.8941	$138.89	$138.90	$138.90
Purchase #4	$24.57	11.337%	$27.3555	$27.36	$27.35	$27.40
Purchase #5	$36.55	12.127%	$40.9824	$40.98	$41.00	$41.00
Purchase #6	$214.45	13.220%	$242.8003	$242.80	$242.80	$242.80
Purchase #7	$48.33	8.853%	$52.6087	$52.61	$52.60	$52.60
7 purchase totals =	$509.68		$569.2027	$569.20	$569.20	$569.20