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	$85.27	6.599%	$90.897	$90.90	$90.90	$90.90
Purchase #2	$249.74	8.191%	$270.1962	$270.20	$270.20	$270.20
Purchase #3	$79.57	10.174%	$87.6655	$87.67	$87.65	$87.70
Purchase #4	$72.67	7.405%	$78.0512	$78.05	$78.05	$78.10
Purchase #5	$168.62	7.840%	$181.8398	$181.84	$181.85	$181.80
Purchase #6	$42.65	4.730%	$44.6673	$44.67	$44.65	$44.70
Purchase #7	$190.88	10.311%	$210.5616	$210.56	$210.55	$210.60
7 purchase totals =	$889.40		$963.8786	$963.89	$963.85	$964.00