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	$149.88	6.284%	$159.2985	$159.30	$159.30	$159.30
Purchase #2	$167.82	7.126%	$179.7789	$179.78	$179.80	$179.80
Purchase #3	$24.57	12.709%	$27.6926	$27.69	$27.70	$27.70
Purchase #4	$10.49	11.601%	$11.7069	$11.71	$11.70	$11.70
Purchase #5	$167.40	10.423%	$184.8481	$184.85	$184.85	$184.80
Purchase #6	$139.47	5.319%	$146.8884	$146.89	$146.90	$146.90
Purchase #7	$124.87	5.447%	$131.6717	$131.67	$131.65	$131.70
7 purchase totals =	$784.50		$841.8851	$841.89	$841.90	$841.90