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	$68.76	4.837%	$72.0859	$72.09	$72.10	$72.10
Purchase #2	$101.34	3.692%	$105.0815	$105.08	$105.10	$105.10
Purchase #3	$186.93	12.483%	$210.2645	$210.26	$210.25	$210.30
Purchase #4	$72.59	8.582%	$78.8197	$78.82	$78.80	$78.80
Purchase #5	$120.96	6.642%	$128.9942	$128.99	$129.00	$129.00
Purchase #6	$23.86	13.820%	$27.1575	$27.16	$27.15	$27.20
Purchase #7	$24.73	12.213%	$27.7503	$27.75	$27.75	$27.80
7 purchase totals =	$599.17		$650.1536	$650.15	$650.15	$650.30