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	$214.56	4.764%	$224.7816	$224.78	$224.80	$224.80
Purchase #2	$100.50	3.319%	$103.8356	$103.84	$103.85	$103.80
Purchase #3	$65.39	8.818%	$71.1561	$71.16	$71.15	$71.20
Purchase #4	$21.61	11.711%	$24.1407	$24.14	$24.15	$24.10
Purchase #5	$176.35	6.818%	$188.3735	$188.37	$188.35	$188.40
Purchase #6	$6.50	10.322%	$7.1709	$7.17	$7.15	$7.20
Purchase #7	$103.63	12.840%	$116.9361	$116.94	$116.95	$116.90
7 purchase totals =	$688.54		$736.3945	$736.40	$736.40	$736.40