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	$123.39	10.836%	$136.7605	$136.76	$136.75	$136.80
Purchase #2	$219.25	3.638%	$227.2263	$227.23	$227.25	$227.20
Purchase #3	$156.25	12.453%	$175.7078	$175.71	$175.70	$175.70
Purchase #4	$90.72	10.364%	$100.1222	$100.12	$100.10	$100.10
Purchase #5	$119.86	3.201%	$123.6967	$123.70	$123.70	$123.70
Purchase #6	$125.39	11.262%	$139.5114	$139.51	$139.50	$139.50
Purchase #7	$166.92	7.796%	$179.9331	$179.93	$179.95	$179.90
7 purchase totals =	$1,001.78		$1,082.9580	$1,082.96	$1,082.95	$1,082.90