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	$132.59	5.712%	$140.1635	$140.16	$140.15	$140.20
Purchase #2	$86.74	4.109%	$90.3041	$90.30	$90.30	$90.30
Purchase #3	$6.52	7.378%	$7.001	$7.00	$7.00	$7.00
Purchase #4	$59.93	6.399%	$63.7649	$63.76	$63.75	$63.80
Purchase #5	$215.43	10.601%	$238.2677	$238.27	$238.25	$238.30
Purchase #6	$217.40	8.473%	$235.8203	$235.82	$235.80	$235.80
Purchase #7	$30.97	12.575%	$34.8645	$34.86	$34.85	$34.90
7 purchase totals =	$749.58		$810.1860	$810.17	$810.10	$810.30