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	$231.81	12.240%	$260.1835	$260.18	$260.20	$260.20
Purchase #2	$75.37	4.672%	$78.8913	$78.89	$78.90	$78.90
Purchase #3	$46.26	8.291%	$50.0954	$50.10	$50.10	$50.10
Purchase #4	$201.66	10.671%	$223.1791	$223.18	$223.20	$223.20
Purchase #5	$41.75	9.116%	$45.5559	$45.56	$45.55	$45.60
Purchase #6	$127.61	5.745%	$134.9412	$134.94	$134.95	$134.90
Purchase #7	$134.47	13.713%	$152.9099	$152.91	$152.90	$152.90
7 purchase totals =	$858.93		$945.7563	$945.76	$945.80	$945.80