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	$50.71	4.171%	$52.8251	$52.83	$52.85	$52.80
Purchase #2	$71.62	9.477%	$78.4074	$78.41	$78.40	$78.40
Purchase #3	$111.41	7.819%	$120.1211	$120.12	$120.10	$120.10
Purchase #4	$180.54	6.836%	$192.8817	$192.88	$192.90	$192.90
Purchase #5	$128.71	6.107%	$136.5703	$136.57	$136.55	$136.60
Purchase #6	$105.62	13.424%	$119.7984	$119.80	$119.80	$119.80
Purchase #7	$39.43	5.497%	$41.5975	$41.60	$41.60	$41.60
7 purchase totals =	$688.04		$742.2015	$742.21	$742.20	$742.20