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	$203.31	12.791%	$229.3154	$229.32	$229.30	$229.30
Purchase #2	$197.72	8.320%	$214.1703	$214.17	$214.15	$214.20
Purchase #3	$196.59	10.676%	$217.5779	$217.58	$217.60	$217.60
Purchase #4	$105.54	6.238%	$112.1236	$112.12	$112.10	$112.10
Purchase #5	$36.36	12.350%	$40.8505	$40.85	$40.85	$40.90
Purchase #6	$77.46	5.677%	$81.8574	$81.86	$81.85	$81.90
Purchase #7	$84.86	5.804%	$89.7853	$89.79	$89.80	$89.80
7 purchase totals =	$901.84		$985.6804	$985.69	$985.65	$985.80