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	$139.98	11.693%	$156.3479	$156.35	$156.35	$156.30
Purchase #2	$181.34	3.183%	$187.1121	$187.11	$187.10	$187.10
Purchase #3	$156.94	4.818%	$164.5014	$164.50	$164.50	$164.50
Purchase #4	$167.64	12.601%	$188.7643	$188.76	$188.75	$188.80
Purchase #5	$123.63	7.518%	$132.9245	$132.92	$132.90	$132.90
Purchase #6	$33.63	13.224%	$38.0772	$38.08	$38.10	$38.10
Purchase #7	$208.50	9.624%	$228.566	$228.57	$228.55	$228.60
7 purchase totals =	$1,011.66		$1,096.2934	$1,096.29	$1,096.25	$1,096.30