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	$240.33	3.609%	$249.0035	$249.00	$249.00	$249.00
Purchase #2	$112.46	6.108%	$119.3291	$119.33	$119.35	$119.30
Purchase #3	$168.47	10.370%	$185.9403	$185.94	$185.95	$185.90
Purchase #4	$55.58	6.263%	$59.061	$59.06	$59.05	$59.10
Purchase #5	$12.47	4.199%	$12.9936	$12.99	$13.00	$13.00
Purchase #6	$138.62	8.687%	$150.6619	$150.66	$150.65	$150.70
Purchase #7	$87.89	5.700%	$92.8997	$92.90	$92.90	$92.90
7 purchase totals =	$815.82		$869.8891	$869.88	$869.90	$869.90