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	$29.29	6.560%	$31.2114	$31.21	$31.20	$31.20
Purchase #2	$55.50	11.843%	$62.0729	$62.07	$62.05	$62.10
Purchase #3	$164.81	4.258%	$171.8276	$171.83	$171.85	$171.80
Purchase #4	$116.37	9.403%	$127.3123	$127.31	$127.30	$127.30
Purchase #5	$114.53	3.303%	$118.3129	$118.31	$118.30	$118.30
Purchase #6	$156.84	12.563%	$176.5438	$176.54	$176.55	$176.50
Purchase #7	$131.98	6.575%	$140.6577	$140.66	$140.65	$140.70
7 purchase totals =	$769.32		$827.9386	$827.93	$827.90	$827.90