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	$50.59	6.751%	$54.0053	$54.01	$54.00	$54.00
Purchase #2	$187.70	4.582%	$196.3004	$196.30	$196.30	$196.30
Purchase #3	$55.84	7.246%	$59.8862	$59.89	$59.90	$59.90
Purchase #4	$25.72	6.411%	$27.3689	$27.37	$27.35	$27.40
Purchase #5	$27.96	4.145%	$29.1189	$29.12	$29.10	$29.10
Purchase #6	$231.45	3.182%	$238.8147	$238.81	$238.80	$238.80
Purchase #7	$64.51	5.468%	$68.0374	$68.04	$68.05	$68.00
7 purchase totals =	$643.77		$673.5318	$673.54	$673.50	$673.50