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	$80.73	10.443%	$89.1606	$89.16	$89.15	$89.20
Purchase #2	$204.31	7.406%	$219.4412	$219.44	$219.45	$219.40
Purchase #3	$28.52	11.686%	$31.8528	$31.85	$31.85	$31.90
Purchase #4	$103.86	3.822%	$107.8295	$107.83	$107.85	$107.80
Purchase #5	$21.71	10.298%	$23.9457	$23.95	$23.95	$23.90
Purchase #6	$229.57	8.776%	$249.7171	$249.72	$249.70	$249.70
Purchase #7	$33.93	4.380%	$35.4161	$35.42	$35.40	$35.40
7 purchase totals =	$702.63		$757.3630	$757.37	$757.35	$757.30