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	$170.93	8.752%	$185.8898	$185.89	$185.90	$185.90
Purchase #2	$142.29	9.179%	$155.3508	$155.35	$155.35	$155.40
Purchase #3	$123.28	6.462%	$131.2464	$131.25	$131.25	$131.20
Purchase #4	$195.80	6.687%	$208.8931	$208.89	$208.90	$208.90
Purchase #5	$143.96	13.619%	$163.5659	$163.57	$163.55	$163.60
Purchase #6	$177.70	7.430%	$190.9031	$190.90	$190.90	$190.90
Purchase #7	$50.82	8.146%	$54.9598	$54.96	$54.95	$55.00
7 purchase totals =	$1,004.78		$1,090.8089	$1,090.81	$1,090.80	$1,090.90