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	$36.84	4.759%	$38.5932	$38.59	$38.60	$38.60
Purchase #2	$246.76	11.382%	$274.8462	$274.85	$274.85	$274.80
Purchase #3	$102.75	5.225%	$108.1187	$108.12	$108.10	$108.10
Purchase #4	$191.80	4.415%	$200.268	$200.27	$200.25	$200.30
Purchase #5	$228.81	9.317%	$250.1282	$250.13	$250.15	$250.10
Purchase #6	$81.86	9.558%	$89.6842	$89.68	$89.70	$89.70
Purchase #7	$165.35	8.825%	$179.9421	$179.94	$179.95	$179.90
7 purchase totals =	$1,054.17		$1,141.5806	$1,141.58	$1,141.60	$1,141.50