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	$37.39	11.233%	$41.59	$41.59	$41.60	$41.60
Purchase #2	$26.64	10.870%	$29.5358	$29.54	$29.55	$29.50
Purchase #3	$121.39	8.471%	$131.6729	$131.67	$131.65	$131.70
Purchase #4	$176.36	11.460%	$196.5709	$196.57	$196.55	$196.60
Purchase #5	$88.96	13.650%	$101.103	$101.10	$101.10	$101.10
Purchase #6	$169.86	10.209%	$187.201	$187.20	$187.20	$187.20
Purchase #7	$75.38	11.327%	$83.9183	$83.92	$83.90	$83.90
7 purchase totals =	$695.98		$771.5919	$771.59	$771.55	$771.60