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	$12.59	6.417%	$13.3979	$13.40	$13.40	$13.40
Purchase #2	$198.93	12.596%	$223.9872	$223.99	$224.00	$224.00
Purchase #3	$176.43	7.769%	$190.1368	$190.14	$190.15	$190.10
Purchase #4	$174.40	3.667%	$180.7952	$180.80	$180.80	$180.80
Purchase #5	$152.93	7.223%	$163.9761	$163.98	$164.00	$164.00
Purchase #6	$215.52	9.187%	$235.3198	$235.32	$235.30	$235.30
Purchase #7	$65.72	10.818%	$72.8296	$72.83	$72.85	$72.80
7 purchase totals =	$996.52		$1,080.4426	$1,080.46	$1,080.50	$1,080.40