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	$57.43	13.801%	$65.3559	$65.36	$65.35	$65.40
Purchase #2	$141.65	7.456%	$152.2114	$152.21	$152.20	$152.20
Purchase #3	$126.62	3.850%	$131.4949	$131.49	$131.50	$131.50
Purchase #4	$78.33	6.138%	$83.1379	$83.14	$83.15	$83.10
Purchase #5	$35.89	12.758%	$40.4688	$40.47	$40.45	$40.50
Purchase #6	$6.44	4.671%	$6.7408	$6.74	$6.75	$6.70
Purchase #7	$113.82	7.723%	$122.6103	$122.61	$122.60	$122.60
7 purchase totals =	$560.18		$602.0200	$602.02	$602.00	$602.00