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	$232.97	11.563%	$259.9083	$259.91	$259.90	$259.90
Purchase #2	$205.87	5.236%	$216.6494	$216.65	$216.65	$216.60
Purchase #3	$159.51	7.650%	$171.7125	$171.71	$171.70	$171.70
Purchase #4	$250.35	8.487%	$271.5972	$271.60	$271.60	$271.60
Purchase #5	$212.35	4.785%	$222.5109	$222.51	$222.50	$222.50
Purchase #6	$89.74	13.378%	$101.7454	$101.75	$101.75	$101.70
Purchase #7	$80.82	12.160%	$90.6477	$90.65	$90.65	$90.60
7 purchase totals =	$1,231.61		$1,334.7714	$1,334.78	$1,334.75	$1,334.60