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	$37.78	13.223%	$42.7756	$42.78	$42.80	$42.80
Purchase #2	$145.98	12.829%	$164.7078	$164.71	$164.70	$164.70
Purchase #3	$165.67	8.484%	$179.7254	$179.73	$179.75	$179.70
Purchase #4	$238.68	6.710%	$254.6954	$254.70	$254.70	$254.70
Purchase #5	$92.34	9.532%	$101.1418	$101.14	$101.15	$101.10
Purchase #6	$78.55	5.194%	$82.6299	$82.63	$82.65	$82.60
Purchase #7	$31.30	6.778%	$33.4215	$33.42	$33.40	$33.40
7 purchase totals =	$790.30		$859.0974	$859.11	$859.15	$859.00