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	$101.30	11.206%	$112.6517	$112.65	$112.65	$112.70
Purchase #2	$129.84	5.619%	$137.1357	$137.14	$137.15	$137.10
Purchase #3	$57.49	12.856%	$64.8809	$64.88	$64.90	$64.90
Purchase #4	$192.56	9.282%	$210.4334	$210.43	$210.45	$210.40
Purchase #5	$57.69	3.808%	$59.8868	$59.89	$59.90	$59.90
Purchase #6	$242.93	12.241%	$272.6671	$272.67	$272.65	$272.70
Purchase #7	$115.29	4.402%	$120.3651	$120.37	$120.35	$120.40
7 purchase totals =	$897.10		$978.0207	$978.03	$978.05	$978.10