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	$238.88	7.429%	$256.6264	$256.63	$256.65	$256.60
Purchase #2	$217.40	13.416%	$246.5664	$246.57	$246.55	$246.60
Purchase #3	$40.48	8.434%	$43.8941	$43.89	$43.90	$43.90
Purchase #4	$13.99	12.613%	$15.7546	$15.75	$15.75	$15.80
Purchase #5	$72.91	8.718%	$79.2663	$79.27	$79.25	$79.30
Purchase #6	$57.86	3.484%	$59.8758	$59.88	$59.90	$59.90
Purchase #7	$132.99	11.207%	$147.8942	$147.89	$147.90	$147.90
7 purchase totals =	$774.51		$849.8778	$849.88	$849.90	$850.00