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	$37.90	12.321%	$42.5697	$42.57	$42.55	$42.60
Purchase #2	$124.31	7.301%	$133.3859	$133.39	$133.40	$133.40
Purchase #3	$180.69	11.192%	$200.9128	$200.91	$200.90	$200.90
Purchase #4	$38.76	11.105%	$43.0643	$43.06	$43.05	$43.10
Purchase #5	$234.91	7.851%	$253.3528	$253.35	$253.35	$253.40
Purchase #6	$245.98	6.212%	$261.2603	$261.26	$261.25	$261.30
Purchase #7	$238.86	6.118%	$253.4735	$253.47	$253.45	$253.50
7 purchase totals =	$1,101.41		$1,188.0193	$1,188.01	$1,187.95	$1,188.20