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	$89.27	7.756%	$96.1938	$96.19	$96.20	$96.20
Purchase #2	$103.86	11.231%	$115.5245	$115.52	$115.50	$115.50
Purchase #3	$216.65	5.228%	$227.9765	$227.98	$228.00	$228.00
Purchase #4	$250.80	4.279%	$261.5317	$261.53	$261.55	$261.50
Purchase #5	$6.51	5.225%	$6.8501	$6.85	$6.85	$6.90
Purchase #6	$78.60	4.802%	$82.3744	$82.37	$82.35	$82.40
Purchase #7	$177.72	6.853%	$189.8992	$189.90	$189.90	$189.90
7 purchase totals =	$923.41		$980.3502	$980.34	$980.35	$980.40