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	$37.29	9.417%	$40.8016	$40.80	$40.80	$40.80
Purchase #2	$35.79	6.498%	$38.1156	$38.12	$38.10	$38.10
Purchase #3	$32.44	7.294%	$34.8062	$34.81	$34.80	$34.80
Purchase #4	$50.94	3.381%	$52.6623	$52.66	$52.65	$52.70
Purchase #5	$215.77	3.644%	$223.6327	$223.63	$223.65	$223.60
Purchase #6	$66.37	8.613%	$72.0864	$72.09	$72.10	$72.10
Purchase #7	$175.67	5.546%	$185.4127	$185.41	$185.40	$185.40
7 purchase totals =	$614.27		$647.5175	$647.52	$647.50	$647.50