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	$16.69	11.173%	$18.5548	$18.55	$18.55	$18.60
Purchase #2	$230.59	6.157%	$244.7874	$244.79	$244.80	$244.80
Purchase #3	$186.38	5.577%	$196.7744	$196.77	$196.75	$196.80
Purchase #4	$62.39	11.249%	$69.4083	$69.41	$69.40	$69.40
Purchase #5	$188.60	12.666%	$212.4881	$212.49	$212.50	$212.50
Purchase #6	$181.89	10.154%	$200.3591	$200.36	$200.35	$200.40
Purchase #7	$131.43	4.226%	$136.9842	$136.98	$137.00	$137.00
7 purchase totals =	$997.97		$1,079.3563	$1,079.35	$1,079.35	$1,079.50