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	$181.56	8.311%	$196.6495	$196.65	$196.65	$196.60
Purchase #2	$176.41	7.609%	$189.833	$189.83	$189.85	$189.80
Purchase #3	$106.56	13.139%	$120.5609	$120.56	$120.55	$120.60
Purchase #4	$120.64	9.298%	$131.8571	$131.86	$131.85	$131.90
Purchase #5	$117.91	11.105%	$131.0039	$131.00	$131.00	$131.00
Purchase #6	$13.90	6.648%	$14.8241	$14.82	$14.80	$14.80
Purchase #7	$29.67	6.247%	$31.5235	$31.52	$31.50	$31.50
7 purchase totals =	$746.65		$816.2520	$816.24	$816.20	$816.20