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	$219.73	9.315%	$240.1978	$240.20	$240.20	$240.20
Purchase #2	$91.76	13.586%	$104.2265	$104.23	$104.25	$104.20
Purchase #3	$76.27	12.121%	$85.5147	$85.51	$85.50	$85.50
Purchase #4	$200.70	4.710%	$210.153	$210.15	$210.15	$210.20
Purchase #5	$164.55	8.648%	$178.7803	$178.78	$178.80	$178.80
Purchase #6	$167.36	6.364%	$178.0108	$178.01	$178.00	$178.00
Purchase #7	$71.74	9.624%	$78.6443	$78.64	$78.65	$78.60
7 purchase totals =	$992.11		$1,075.5274	$1,075.52	$1,075.55	$1,075.50