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	$24.69	11.319%	$27.4847	$27.48	$27.50	$27.50
Purchase #2	$179.32	11.584%	$200.0924	$200.09	$200.10	$200.10
Purchase #3	$67.53	11.620%	$75.377	$75.38	$75.40	$75.40
Purchase #4	$56.29	5.785%	$59.5464	$59.55	$59.55	$59.50
Purchase #5	$107.29	11.672%	$119.8129	$119.81	$119.80	$119.80
Purchase #6	$23.98	10.872%	$26.5871	$26.59	$26.60	$26.60
Purchase #7	$179.54	4.392%	$187.4254	$187.43	$187.45	$187.40
7 purchase totals =	$638.64		$696.3259	$696.33	$696.40	$696.30