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	$39.64	4.558%	$41.4468	$41.45	$41.45	$41.40
Purchase #2	$180.62	10.144%	$198.9421	$198.94	$198.95	$198.90
Purchase #3	$218.83	9.192%	$238.9449	$238.94	$238.95	$238.90
Purchase #4	$250.39	7.826%	$269.9855	$269.99	$270.00	$270.00
Purchase #5	$134.50	3.179%	$138.7758	$138.78	$138.80	$138.80
Purchase #6	$39.79	13.601%	$45.2018	$45.20	$45.20	$45.20
Purchase #7	$77.35	6.853%	$82.6508	$82.65	$82.65	$82.70
7 purchase totals =	$941.12		$1,015.9477	$1,015.95	$1,016.00	$1,015.90