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	$138.25	3.632%	$143.2712	$143.27	$143.25	$143.30
Purchase #2	$167.33	6.570%	$178.3236	$178.32	$178.30	$178.30
Purchase #3	$234.49	7.742%	$252.6442	$252.64	$252.65	$252.60
Purchase #4	$148.94	13.297%	$168.7446	$168.74	$168.75	$168.70
Purchase #5	$54.96	8.647%	$59.7124	$59.71	$59.70	$59.70
Purchase #6	$84.72	7.227%	$90.8427	$90.84	$90.85	$90.80
Purchase #7	$75.35	6.197%	$80.0194	$80.02	$80.00	$80.00
7 purchase totals =	$904.04		$973.5581	$973.54	$973.50	$973.40