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	$84.83	10.215%	$93.4954	$93.50	$93.50	$93.50
Purchase #2	$189.36	8.688%	$205.8116	$205.81	$205.80	$205.80
Purchase #3	$57.90	11.119%	$64.3379	$64.34	$64.35	$64.30
Purchase #4	$168.45	8.380%	$182.5661	$182.57	$182.55	$182.60
Purchase #5	$106.85	12.166%	$119.8494	$119.85	$119.85	$119.80
Purchase #6	$231.30	10.693%	$256.0329	$256.03	$256.05	$256.00
Purchase #7	$72.54	11.326%	$80.7559	$80.76	$80.75	$80.80
7 purchase totals =	$911.23		$1,002.8492	$1,002.86	$1,002.85	$1,002.80