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	$201.40	9.388%	$220.3074	$220.31	$220.30	$220.30
Purchase #2	$48.83	4.636%	$51.0938	$51.09	$51.10	$51.10
Purchase #3	$99.87	3.476%	$103.3415	$103.34	$103.35	$103.30
Purchase #4	$237.33	12.659%	$267.3736	$267.37	$267.35	$267.40
Purchase #5	$243.61	12.468%	$273.9833	$273.98	$274.00	$274.00
Purchase #6	$27.77	5.417%	$29.2743	$29.27	$29.25	$29.30
Purchase #7	$66.57	10.381%	$73.4806	$73.48	$73.50	$73.50
7 purchase totals =	$925.38		$1,018.8545	$1,018.84	$1,018.85	$1,018.90