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	$12.89	7.171%	$13.8143	$13.81	$13.80	$13.80
Purchase #2	$176.53	11.546%	$196.9122	$196.91	$196.90	$196.90
Purchase #3	$148.32	10.751%	$164.2659	$164.27	$164.25	$164.30
Purchase #4	$108.61	3.228%	$112.1159	$112.12	$112.10	$112.10
Purchase #5	$204.39	5.538%	$215.7091	$215.71	$215.70	$215.70
Purchase #6	$105.62	9.645%	$115.807	$115.81	$115.80	$115.80
Purchase #7	$44.39	6.707%	$47.3672	$47.37	$47.35	$47.40
7 purchase totals =	$800.75		$865.9916	$866.00	$865.90	$866.00