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	$74.85	6.296%	$79.5626	$79.56	$79.55	$79.60
Purchase #2	$213.51	10.787%	$236.5413	$236.54	$236.55	$236.50
Purchase #3	$203.29	11.774%	$227.2254	$227.23	$227.25	$227.20
Purchase #4	$152.65	10.365%	$168.4722	$168.47	$168.45	$168.50
Purchase #5	$100.98	9.472%	$110.5448	$110.54	$110.55	$110.50
Purchase #6	$38.51	6.157%	$40.8811	$40.88	$40.90	$40.90
Purchase #7	$96.29	4.646%	$100.7636	$100.76	$100.75	$100.80
7 purchase totals =	$880.08		$963.9910	$963.98	$964.00	$964.00