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	$149.70	7.421%	$160.8092	$160.81	$160.80	$160.80
Purchase #2	$183.28	11.146%	$203.7084	$203.71	$203.70	$203.70
Purchase #3	$249.88	5.431%	$263.451	$263.45	$263.45	$263.50
Purchase #4	$167.95	12.820%	$189.4812	$189.48	$189.50	$189.50
Purchase #5	$124.25	12.153%	$139.3501	$139.35	$139.35	$139.40
Purchase #6	$161.48	6.745%	$172.3718	$172.37	$172.35	$172.40
Purchase #7	$18.90	10.295%	$20.8458	$20.85	$20.85	$20.80
7 purchase totals =	$1,055.44		$1,150.0175	$1,150.02	$1,150.00	$1,150.10