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	$36.50	10.826%	$40.4515	$40.45	$40.45	$40.50
Purchase #2	$130.90	7.540%	$140.7699	$140.77	$140.75	$140.80
Purchase #3	$60.31	13.609%	$68.5176	$68.52	$68.50	$68.50
Purchase #4	$74.40	10.319%	$82.0773	$82.08	$82.10	$82.10
Purchase #5	$246.37	7.415%	$264.6383	$264.64	$264.65	$264.60
Purchase #6	$131.44	13.283%	$148.8992	$148.90	$148.90	$148.90
Purchase #7	$93.42	10.250%	$102.9956	$103.00	$103.00	$103.00
7 purchase totals =	$773.34		$848.3494	$848.36	$848.35	$848.40