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	$31.92	11.529%	$35.6001	$35.60	$35.60	$35.60
Purchase #2	$80.93	10.270%	$89.2415	$89.24	$89.25	$89.20
Purchase #3	$204.60	9.356%	$223.7424	$223.74	$223.75	$223.70
Purchase #4	$176.59	12.401%	$198.4889	$198.49	$198.50	$198.50
Purchase #5	$49.72	8.558%	$53.975	$53.98	$54.00	$54.00
Purchase #6	$188.43	9.229%	$205.8202	$205.82	$205.80	$205.80
Purchase #7	$38.38	11.567%	$42.8194	$42.82	$42.80	$42.80
7 purchase totals =	$770.57		$849.6875	$849.69	$849.70	$849.60