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	$226.47	3.247%	$233.8235	$233.82	$233.80	$233.80
Purchase #2	$45.92	7.842%	$49.521	$49.52	$49.50	$49.50
Purchase #3	$25.55	7.314%	$27.4187	$27.42	$27.40	$27.40
Purchase #4	$154.56	3.466%	$159.917	$159.92	$159.90	$159.90
Purchase #5	$190.84	7.172%	$204.527	$204.53	$204.55	$204.50
Purchase #6	$105.97	12.678%	$119.4049	$119.40	$119.40	$119.40
Purchase #7	$186.59	12.682%	$210.2533	$210.25	$210.25	$210.30
7 purchase totals =	$935.90		$1,004.8654	$1,004.86	$1,004.80	$1,004.80