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	$227.39	11.671%	$253.9287	$253.93	$253.95	$253.90
Purchase #2	$104.51	3.589%	$108.2609	$108.26	$108.25	$108.30
Purchase #3	$34.51	12.166%	$38.7085	$38.71	$38.70	$38.70
Purchase #4	$195.38	4.687%	$204.5375	$204.54	$204.55	$204.50
Purchase #5	$192.51	4.159%	$200.5165	$200.52	$200.50	$200.50
Purchase #6	$100.58	4.112%	$104.7158	$104.72	$104.70	$104.70
Purchase #7	$114.50	4.591%	$119.7567	$119.76	$119.75	$119.80
7 purchase totals =	$969.38		$1,030.4246	$1,030.44	$1,030.40	$1,030.40