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	$84.59	7.294%	$90.76	$90.76	$90.75	$90.80
Purchase #2	$235.29	13.275%	$266.5247	$266.52	$266.50	$266.50
Purchase #3	$119.69	3.401%	$123.7607	$123.76	$123.75	$123.80
Purchase #4	$5.38	3.822%	$5.5856	$5.59	$5.60	$5.60
Purchase #5	$51.92	7.627%	$55.8799	$55.88	$55.90	$55.90
Purchase #6	$201.83	10.602%	$223.228	$223.23	$223.25	$223.20
Purchase #7	$165.43	7.736%	$178.2277	$178.23	$178.25	$178.20
7 purchase totals =	$864.13		$943.9666	$943.97	$944.00	$944.00