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	$54.47	11.152%	$60.5445	$60.54	$60.55	$60.50
Purchase #2	$38.57	4.872%	$40.4491	$40.45	$40.45	$40.40
Purchase #3	$197.62	4.155%	$205.8311	$205.83	$205.85	$205.80
Purchase #4	$238.48	12.468%	$268.2137	$268.21	$268.20	$268.20
Purchase #5	$89.98	9.755%	$98.7575	$98.76	$98.75	$98.80
Purchase #6	$24.54	4.307%	$25.5969	$25.60	$25.60	$25.60
Purchase #7	$164.83	3.759%	$171.026	$171.03	$171.05	$171.00
7 purchase totals =	$808.49		$870.4188	$870.42	$870.45	$870.30