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	$154.56	6.395%	$164.4441	$164.44	$164.45	$164.40
Purchase #2	$158.63	3.729%	$164.5453	$164.55	$164.55	$164.50
Purchase #3	$84.73	7.244%	$90.8678	$90.87	$90.85	$90.90
Purchase #4	$213.35	5.562%	$225.2165	$225.22	$225.20	$225.20
Purchase #5	$184.71	6.133%	$196.0383	$196.04	$196.05	$196.00
Purchase #6	$183.54	11.618%	$204.8637	$204.86	$204.85	$204.90
Purchase #7	$140.73	12.236%	$157.9497	$157.95	$157.95	$157.90
7 purchase totals =	$1,120.25		$1,203.9254	$1,203.93	$1,203.90	$1,203.80