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	$154.54	12.425%	$173.7416	$173.74	$173.75	$173.70
Purchase #2	$42.44	9.264%	$46.3716	$46.37	$46.35	$46.40
Purchase #3	$99.59	13.226%	$112.7618	$112.76	$112.75	$112.80
Purchase #4	$64.76	12.657%	$72.9567	$72.96	$72.95	$73.00
Purchase #5	$64.44	5.244%	$67.8192	$67.82	$67.80	$67.80
Purchase #6	$192.69	6.558%	$205.3266	$205.33	$205.35	$205.30
Purchase #7	$112.97	13.834%	$128.5983	$128.60	$128.60	$128.60
7 purchase totals =	$731.43		$807.5758	$807.58	$807.55	$807.60