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	$79.69	7.151%	$85.3886	$85.39	$85.40	$85.40
Purchase #2	$25.65	7.129%	$27.4786	$27.48	$27.50	$27.50
Purchase #3	$179.70	13.581%	$204.1051	$204.11	$204.10	$204.10
Purchase #4	$76.86	10.788%	$85.1517	$85.15	$85.15	$85.20
Purchase #5	$217.93	3.124%	$224.7381	$224.74	$224.75	$224.70
Purchase #6	$40.50	12.278%	$45.4726	$45.47	$45.45	$45.50
Purchase #7	$83.64	10.664%	$92.5594	$92.56	$92.55	$92.60
7 purchase totals =	$703.97		$764.8941	$764.90	$764.90	$765.00