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	$36.99	11.381%	$41.1998	$41.20	$41.20	$41.20
Purchase #2	$152.65	12.273%	$171.3847	$171.38	$171.40	$171.40
Purchase #3	$135.88	9.300%	$148.5168	$148.52	$148.50	$148.50
Purchase #4	$236.83	10.832%	$262.4834	$262.48	$262.50	$262.50
Purchase #5	$71.54	12.479%	$80.4675	$80.47	$80.45	$80.50
Purchase #6	$51.36	9.834%	$56.4107	$56.41	$56.40	$56.40
Purchase #7	$133.76	13.822%	$152.2483	$152.25	$152.25	$152.20
7 purchase totals =	$819.01		$912.7112	$912.71	$912.70	$912.70