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	$199.87	8.111%	$216.0815	$216.08	$216.10	$216.10
Purchase #2	$126.93	11.295%	$141.2667	$141.27	$141.25	$141.30
Purchase #3	$24.30	11.630%	$27.1261	$27.13	$27.15	$27.10
Purchase #4	$115.48	8.499%	$125.2946	$125.29	$125.30	$125.30
Purchase #5	$102.82	8.259%	$111.3119	$111.31	$111.30	$111.30
Purchase #6	$121.64	4.646%	$127.2914	$127.29	$127.30	$127.30
Purchase #7	$180.93	4.700%	$189.4337	$189.43	$189.45	$189.40
7 purchase totals =	$871.97		$937.8059	$937.80	$937.85	$937.80