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	$8.83	13.326%	$10.0067	$10.01	$10.00	$10.00
Purchase #2	$222.56	9.843%	$244.4666	$244.47	$244.45	$244.50
Purchase #3	$244.73	8.523%	$265.5883	$265.59	$265.60	$265.60
Purchase #4	$75.96	3.279%	$78.4507	$78.45	$78.45	$78.50
Purchase #5	$192.28	8.184%	$208.0162	$208.02	$208.00	$208.00
Purchase #6	$38.72	7.324%	$41.5559	$41.56	$41.55	$41.60
Purchase #7	$86.39	3.300%	$89.2409	$89.24	$89.25	$89.20
7 purchase totals =	$869.47		$937.3253	$937.34	$937.30	$937.40