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	$144.93	13.252%	$164.1361	$164.14	$164.15	$164.10
Purchase #2	$42.40	13.484%	$48.1172	$48.12	$48.10	$48.10
Purchase #3	$25.43	11.222%	$28.2838	$28.28	$28.30	$28.30
Purchase #4	$101.98	12.460%	$114.6867	$114.69	$114.70	$114.70
Purchase #5	$17.43	13.822%	$19.8392	$19.84	$19.85	$19.80
Purchase #6	$54.53	9.393%	$59.652	$59.65	$59.65	$59.70
Purchase #7	$128.44	11.110%	$142.7097	$142.71	$142.70	$142.70
7 purchase totals =	$515.14		$577.4247	$577.43	$577.45	$577.40