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	$54.71	9.506%	$59.9107	$59.91	$59.90	$59.90
Purchase #2	$125.41	9.840%	$137.7503	$137.75	$137.75	$137.80
Purchase #3	$177.39	4.331%	$185.0728	$185.07	$185.05	$185.10
Purchase #4	$115.87	5.741%	$122.5221	$122.52	$122.50	$122.50
Purchase #5	$228.49	13.771%	$259.9554	$259.96	$259.95	$260.00
Purchase #6	$29.91	11.588%	$33.376	$33.38	$33.40	$33.40
Purchase #7	$67.76	6.591%	$72.2261	$72.23	$72.25	$72.20
7 purchase totals =	$799.54		$870.8134	$870.82	$870.80	$870.90