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	$73.70	8.294%	$79.8127	$79.81	$79.80	$79.80
Purchase #2	$112.98	11.433%	$125.897	$125.90	$125.90	$125.90
Purchase #3	$16.68	10.712%	$18.4668	$18.47	$18.45	$18.50
Purchase #4	$79.33	5.606%	$83.7772	$83.78	$83.80	$83.80
Purchase #5	$170.92	10.508%	$188.8803	$188.88	$188.90	$188.90
Purchase #6	$183.68	7.128%	$196.7727	$196.77	$196.75	$196.80
Purchase #7	$116.83	3.427%	$120.8338	$120.83	$120.85	$120.80
7 purchase totals =	$754.12		$814.4405	$814.44	$814.45	$814.50