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	$48.42	10.648%	$53.5758	$53.58	$53.60	$53.60
Purchase #2	$164.73	3.698%	$170.8217	$170.82	$170.80	$170.80
Purchase #3	$121.33	7.596%	$130.5462	$130.55	$130.55	$130.50
Purchase #4	$85.76	4.444%	$89.5712	$89.57	$89.55	$89.60
Purchase #5	$54.57	8.674%	$59.3034	$59.30	$59.30	$59.30
Purchase #6	$206.76	13.484%	$234.6395	$234.64	$234.65	$234.60
Purchase #7	$196.29	11.111%	$218.0998	$218.10	$218.10	$218.10
7 purchase totals =	$877.86		$956.5576	$956.56	$956.55	$956.50