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	$231.65	3.601%	$239.9917	$239.99	$240.00	$240.00
Purchase #2	$99.40	5.455%	$104.8223	$104.82	$104.80	$104.80
Purchase #3	$30.41	3.789%	$31.5622	$31.56	$31.55	$31.60
Purchase #4	$136.85	13.444%	$155.2481	$155.25	$155.25	$155.20
Purchase #5	$141.71	7.710%	$152.6358	$152.64	$152.65	$152.60
Purchase #6	$139.82	3.769%	$145.0898	$145.09	$145.10	$145.10
Purchase #7	$33.68	12.279%	$37.8156	$37.82	$37.80	$37.80
7 purchase totals =	$813.52		$867.1655	$867.17	$867.15	$867.10