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	$203.73	6.250%	$216.4631	$216.46	$216.45	$216.50
Purchase #2	$169.74	12.777%	$191.4277	$191.43	$191.45	$191.40
Purchase #3	$238.77	6.812%	$255.035	$255.04	$255.05	$255.00
Purchase #4	$105.58	12.659%	$118.9454	$118.95	$118.95	$118.90
Purchase #5	$43.56	13.377%	$49.387	$49.39	$49.40	$49.40
Purchase #6	$86.87	3.180%	$89.6325	$89.63	$89.65	$89.60
Purchase #7	$112.56	5.751%	$119.0333	$119.03	$119.05	$119.00
7 purchase totals =	$960.81		$1,039.9240	$1,039.93	$1,040.00	$1,039.80