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	$19.77	3.728%	$20.507	$20.51	$20.50	$20.50
Purchase #2	$77.89	9.308%	$85.14	$85.14	$85.15	$85.10
Purchase #3	$33.62	8.548%	$36.4938	$36.49	$36.50	$36.50
Purchase #4	$192.49	9.530%	$210.8343	$210.83	$210.85	$210.80
Purchase #5	$51.63	6.243%	$54.8533	$54.85	$54.85	$54.90
Purchase #6	$165.81	7.314%	$177.9373	$177.94	$177.95	$177.90
Purchase #7	$100.67	8.258%	$108.9833	$108.98	$109.00	$109.00
7 purchase totals =	$641.88		$694.7490	$694.74	$694.80	$694.70