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	$204.64	6.693%	$218.3366	$218.34	$218.35	$218.30
Purchase #2	$141.54	10.459%	$156.3437	$156.34	$156.35	$156.30
Purchase #3	$118.95	4.765%	$124.618	$124.62	$124.60	$124.60
Purchase #4	$52.81	5.290%	$55.6036	$55.60	$55.60	$55.60
Purchase #5	$43.50	8.656%	$47.2654	$47.27	$47.25	$47.30
Purchase #6	$99.63	5.859%	$105.4673	$105.47	$105.45	$105.50
Purchase #7	$62.52	8.134%	$67.6054	$67.61	$67.60	$67.60
7 purchase totals =	$723.59		$775.2400	$775.25	$775.20	$775.20