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	$132.89	10.270%	$146.5378	$146.54	$146.55	$146.50
Purchase #2	$247.64	13.168%	$280.2492	$280.25	$280.25	$280.20
Purchase #3	$71.61	9.194%	$78.1938	$78.19	$78.20	$78.20
Purchase #4	$8.39	12.388%	$9.4294	$9.43	$9.45	$9.40
Purchase #5	$236.45	11.346%	$263.2776	$263.28	$263.30	$263.30
Purchase #6	$79.75	12.547%	$89.7562	$89.76	$89.75	$89.80
Purchase #7	$155.84	5.460%	$164.3489	$164.35	$164.35	$164.30
7 purchase totals =	$932.57		$1,031.7929	$1,031.80	$1,031.85	$1,031.70