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	$81.41	11.495%	$90.7681	$90.77	$90.75	$90.80
Purchase #2	$164.75	11.494%	$183.6864	$183.69	$183.70	$183.70
Purchase #3	$57.59	10.734%	$63.7717	$63.77	$63.75	$63.80
Purchase #4	$118.97	10.579%	$131.5558	$131.56	$131.55	$131.60
Purchase #5	$90.50	8.743%	$98.4124	$98.41	$98.40	$98.40
Purchase #6	$136.48	6.256%	$145.0182	$145.02	$145.00	$145.00
Purchase #7	$159.33	12.483%	$179.2192	$179.22	$179.20	$179.20
7 purchase totals =	$809.03		$892.4318	$892.44	$892.35	$892.50