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	$35.56	7.855%	$38.3532	$38.35	$38.35	$38.40
Purchase #2	$83.73	9.667%	$91.8242	$91.82	$91.80	$91.80
Purchase #3	$185.77	5.792%	$196.5298	$196.53	$196.55	$196.50
Purchase #4	$166.40	11.700%	$185.8688	$185.87	$185.85	$185.90
Purchase #5	$60.97	10.600%	$67.4328	$67.43	$67.45	$67.40
Purchase #6	$71.32	12.533%	$80.2585	$80.26	$80.25	$80.30
Purchase #7	$43.80	13.624%	$49.7673	$49.77	$49.75	$49.80
7 purchase totals =	$647.55		$710.0346	$710.03	$710.00	$710.10