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	$86.50	3.742%	$89.7368	$89.74	$89.75	$89.70
Purchase #2	$197.72	9.861%	$217.2172	$217.22	$217.20	$217.20
Purchase #3	$206.90	10.701%	$229.0404	$229.04	$229.05	$229.00
Purchase #4	$216.70	10.119%	$238.6279	$238.63	$238.65	$238.60
Purchase #5	$77.59	11.392%	$86.4291	$86.43	$86.45	$86.40
Purchase #6	$56.52	4.514%	$59.0713	$59.07	$59.05	$59.10
Purchase #7	$72.47	7.804%	$78.1256	$78.13	$78.15	$78.10
7 purchase totals =	$914.40		$998.2483	$998.26	$998.30	$998.10