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	$123.46	10.180%	$136.0282	$136.03	$136.05	$136.00
Purchase #2	$102.63	8.300%	$111.1483	$111.15	$111.15	$111.10
Purchase #3	$221.43	4.351%	$231.0644	$231.06	$231.05	$231.10
Purchase #4	$179.52	8.332%	$194.4776	$194.48	$194.50	$194.50
Purchase #5	$29.80	13.458%	$33.8105	$33.81	$33.80	$33.80
Purchase #6	$122.90	11.417%	$136.9315	$136.93	$136.95	$136.90
Purchase #7	$88.72	3.387%	$91.7249	$91.72	$91.70	$91.70
7 purchase totals =	$868.46		$935.1854	$935.18	$935.20	$935.10