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	$33.37	13.750%	$37.9584	$37.96	$37.95	$38.00
Purchase #2	$109.57	4.870%	$114.9061	$114.91	$114.90	$114.90
Purchase #3	$138.78	4.173%	$144.5713	$144.57	$144.55	$144.60
Purchase #4	$164.98	7.817%	$177.8765	$177.88	$177.90	$177.90
Purchase #5	$80.70	10.665%	$89.3067	$89.31	$89.30	$89.30
Purchase #6	$13.33	12.692%	$15.0218	$15.02	$15.00	$15.00
Purchase #7	$65.93	8.762%	$71.7068	$71.71	$71.70	$71.70
7 purchase totals =	$606.66		$651.3476	$651.36	$651.30	$651.40