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	$53.44	10.591%	$59.0998	$59.10	$59.10	$59.10
Purchase #2	$81.83	3.474%	$84.6728	$84.67	$84.65	$84.70
Purchase #3	$57.75	9.651%	$63.3235	$63.32	$63.30	$63.30
Purchase #4	$149.83	11.519%	$167.0889	$167.09	$167.10	$167.10
Purchase #5	$131.65	7.279%	$141.2328	$141.23	$141.25	$141.20
Purchase #6	$203.54	12.759%	$229.5097	$229.51	$229.50	$229.50
Purchase #7	$36.53	13.856%	$41.5916	$41.59	$41.60	$41.60
7 purchase totals =	$714.57		$786.5191	$786.51	$786.50	$786.50