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	$204.84	8.706%	$222.6734	$222.67	$222.65	$222.70
Purchase #2	$214.46	3.779%	$222.5644	$222.56	$222.55	$222.60
Purchase #3	$37.64	4.704%	$39.4106	$39.41	$39.40	$39.40
Purchase #4	$17.56	7.873%	$18.9425	$18.94	$18.95	$18.90
Purchase #5	$113.47	10.680%	$125.5886	$125.59	$125.60	$125.60
Purchase #6	$206.30	12.407%	$231.8956	$231.90	$231.90	$231.90
Purchase #7	$109.40	6.309%	$116.302	$116.30	$116.30	$116.30
7 purchase totals =	$903.67		$977.3771	$977.37	$977.35	$977.40