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	$112.67	5.301%	$118.6426	$118.64	$118.65	$118.60
Purchase #2	$227.98	12.641%	$256.799	$256.80	$256.80	$256.80
Purchase #3	$39.43	6.710%	$42.0758	$42.08	$42.10	$42.10
Purchase #4	$106.29	12.636%	$119.7208	$119.72	$119.70	$119.70
Purchase #5	$180.47	12.154%	$202.4043	$202.40	$202.40	$202.40
Purchase #6	$189.87	3.346%	$196.2231	$196.22	$196.20	$196.20
Purchase #7	$134.78	6.740%	$143.8642	$143.86	$143.85	$143.90
7 purchase totals =	$991.49		$1,079.7298	$1,079.72	$1,079.70	$1,079.70