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	$72.83	7.264%	$78.1204	$78.12	$78.10	$78.10
Purchase #2	$59.56	9.216%	$65.049	$65.05	$65.05	$65.00
Purchase #3	$43.31	3.589%	$44.8644	$44.86	$44.85	$44.90
Purchase #4	$21.28	3.690%	$22.0652	$22.07	$22.05	$22.10
Purchase #5	$38.82	8.222%	$42.0118	$42.01	$42.00	$42.00
Purchase #6	$22.60	10.472%	$24.9667	$24.97	$24.95	$25.00
Purchase #7	$125.98	12.823%	$142.1344	$142.13	$142.15	$142.10
7 purchase totals =	$384.38		$419.2119	$419.21	$419.15	$419.20