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	$138.83	10.577%	$153.514	$153.51	$153.50	$153.50
Purchase #2	$114.63	11.229%	$127.5018	$127.50	$127.50	$127.50
Purchase #3	$19.36	7.453%	$20.8029	$20.80	$20.80	$20.80
Purchase #4	$240.65	12.538%	$270.8227	$270.82	$270.80	$270.80
Purchase #5	$221.37	7.679%	$238.369	$238.37	$238.35	$238.40
Purchase #6	$231.25	6.846%	$247.0814	$247.08	$247.10	$247.10
Purchase #7	$88.81	10.837%	$98.4343	$98.43	$98.45	$98.40
7 purchase totals =	$1,054.90		$1,156.5261	$1,156.51	$1,156.50	$1,156.50