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	$44.99	5.142%	$47.3034	$47.30	$47.30	$47.30
Purchase #2	$116.30	9.649%	$127.5218	$127.52	$127.50	$127.50
Purchase #3	$159.73	8.632%	$173.5179	$173.52	$173.50	$173.50
Purchase #4	$76.79	10.567%	$84.9044	$84.90	$84.90	$84.90
Purchase #5	$122.29	11.490%	$136.3411	$136.34	$136.35	$136.30
Purchase #6	$31.47	12.112%	$35.2816	$35.28	$35.30	$35.30
Purchase #7	$59.29	13.249%	$67.1453	$67.15	$67.15	$67.10
7 purchase totals =	$610.86		$672.0155	$672.01	$672.00	$671.90