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	$71.77	9.810%	$78.8106	$78.81	$78.80	$78.80
Purchase #2	$160.59	12.116%	$180.0471	$180.05	$180.05	$180.00
Purchase #3	$64.99	3.754%	$67.4297	$67.43	$67.45	$67.40
Purchase #4	$36.44	8.342%	$39.4798	$39.48	$39.50	$39.50
Purchase #5	$125.40	13.858%	$142.7779	$142.78	$142.80	$142.80
Purchase #6	$239.63	7.792%	$258.302	$258.30	$258.30	$258.30
Purchase #7	$143.84	4.361%	$150.1129	$150.11	$150.10	$150.10
7 purchase totals =	$842.66		$916.9600	$916.96	$917.00	$916.90