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	$20.53	13.168%	$23.2334	$23.23	$23.25	$23.20
Purchase #2	$79.50	12.552%	$89.4788	$89.48	$89.50	$89.50
Purchase #3	$52.36	3.774%	$54.3361	$54.34	$54.35	$54.30
Purchase #4	$66.56	8.459%	$72.1903	$72.19	$72.20	$72.20
Purchase #5	$202.71	13.159%	$229.3846	$229.38	$229.40	$229.40
Purchase #6	$167.86	5.347%	$176.8355	$176.84	$176.85	$176.80
Purchase #7	$186.82	12.605%	$210.3687	$210.37	$210.35	$210.40
7 purchase totals =	$776.34		$855.8274	$855.83	$855.90	$855.80