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	$223.59	12.204%	$250.8769	$250.88	$250.90	$250.90
Purchase #2	$33.32	9.116%	$36.3575	$36.36	$36.35	$36.40
Purchase #3	$175.79	8.529%	$190.7831	$190.78	$190.80	$190.80
Purchase #4	$126.44	11.664%	$141.188	$141.19	$141.20	$141.20
Purchase #5	$80.29	3.267%	$82.9131	$82.91	$82.90	$82.90
Purchase #6	$153.68	9.668%	$168.5378	$168.54	$168.55	$168.50
Purchase #7	$9.86	5.526%	$10.4049	$10.40	$10.40	$10.40
7 purchase totals =	$802.97		$881.0613	$881.06	$881.10	$881.10