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	$52.79	5.718%	$55.8085	$55.81	$55.80	$55.80
Purchase #2	$151.83	13.695%	$172.6231	$172.62	$172.60	$172.60
Purchase #3	$116.38	7.752%	$125.4018	$125.40	$125.40	$125.40
Purchase #4	$82.48	12.104%	$92.4634	$92.46	$92.45	$92.50
Purchase #5	$139.72	8.627%	$151.7736	$151.77	$151.75	$151.80
Purchase #6	$93.98	4.739%	$98.4337	$98.43	$98.45	$98.40
Purchase #7	$224.33	3.183%	$231.4704	$231.47	$231.45	$231.50
7 purchase totals =	$861.51		$927.9745	$927.96	$927.90	$928.00