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	$37.99	10.817%	$42.0994	$42.10	$42.10	$42.10
Purchase #2	$15.38	6.425%	$16.3682	$16.37	$16.35	$16.40
Purchase #3	$96.87	7.220%	$103.864	$103.86	$103.85	$103.90
Purchase #4	$50.67	12.636%	$57.0727	$57.07	$57.05	$57.10
Purchase #5	$209.87	9.659%	$230.1413	$230.14	$230.15	$230.10
Purchase #6	$182.35	4.119%	$189.861	$189.86	$189.85	$189.90
Purchase #7	$55.54	10.780%	$61.5272	$61.53	$61.55	$61.50
7 purchase totals =	$648.67		$700.9338	$700.93	$700.90	$701.00