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	$119.29	3.509%	$123.4759	$123.48	$123.50	$123.50
Purchase #2	$82.90	11.385%	$92.3382	$92.34	$92.35	$92.30
Purchase #3	$66.98	6.369%	$71.246	$71.25	$71.25	$71.20
Purchase #4	$98.47	12.534%	$110.8122	$110.81	$110.80	$110.80
Purchase #5	$56.96	12.635%	$64.1569	$64.16	$64.15	$64.20
Purchase #6	$179.51	11.348%	$199.8808	$199.88	$199.90	$199.90
Purchase #7	$156.83	12.313%	$176.1405	$176.14	$176.15	$176.10
7 purchase totals =	$760.94		$838.0505	$838.06	$838.10	$838.00