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	$132.61	3.709%	$137.5285	$137.53	$137.55	$137.50
Purchase #2	$37.63	6.326%	$40.0105	$40.01	$40.00	$40.00
Purchase #3	$154.49	11.226%	$171.833	$171.83	$171.85	$171.80
Purchase #4	$145.87	6.827%	$155.8285	$155.83	$155.85	$155.80
Purchase #5	$176.87	13.174%	$200.1709	$200.17	$200.15	$200.20
Purchase #6	$78.55	3.439%	$81.2513	$81.25	$81.25	$81.30
Purchase #7	$165.93	11.791%	$185.4948	$185.49	$185.50	$185.50
7 purchase totals =	$891.95		$972.1175	$972.11	$972.15	$972.10