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	$249.86	6.313%	$265.6337	$265.63	$265.65	$265.60
Purchase #2	$156.57	8.804%	$170.3544	$170.35	$170.35	$170.40
Purchase #3	$146.42	6.869%	$156.4776	$156.48	$156.50	$156.50
Purchase #4	$33.90	11.833%	$37.9114	$37.91	$37.90	$37.90
Purchase #5	$33.38	12.299%	$37.4854	$37.49	$37.50	$37.50
Purchase #6	$106.25	7.842%	$114.5821	$114.58	$114.60	$114.60
Purchase #7	$118.32	11.152%	$131.515	$131.52	$131.50	$131.50
7 purchase totals =	$844.70		$913.9596	$913.96	$914.00	$914.00