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	$29.53	4.556%	$30.8754	$30.88	$30.90	$30.90
Purchase #2	$56.66	11.870%	$63.3855	$63.39	$63.40	$63.40
Purchase #3	$20.65	9.107%	$22.5306	$22.53	$22.55	$22.50
Purchase #4	$177.93	13.449%	$201.8598	$201.86	$201.85	$201.90
Purchase #5	$87.43	3.816%	$90.7663	$90.77	$90.75	$90.80
Purchase #6	$99.90	6.667%	$106.5603	$106.56	$106.55	$106.60
Purchase #7	$78.60	8.833%	$85.5427	$85.54	$85.55	$85.50
7 purchase totals =	$550.70		$601.5206	$601.53	$601.55	$601.60