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	$29.57	7.294%	$31.7268	$31.73	$31.75	$31.70
Purchase #2	$175.37	6.248%	$186.3271	$186.33	$186.35	$186.30
Purchase #3	$128.64	9.646%	$141.0486	$141.05	$141.05	$141.00
Purchase #4	$183.65	9.384%	$200.8837	$200.88	$200.90	$200.90
Purchase #5	$6.32	12.384%	$7.1027	$7.10	$7.10	$7.10
Purchase #6	$50.32	5.587%	$53.1314	$53.13	$53.15	$53.10
Purchase #7	$169.50	10.543%	$187.3704	$187.37	$187.35	$187.40
7 purchase totals =	$743.37		$807.5907	$807.59	$807.65	$807.50