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	$124.97	9.581%	$136.9434	$136.94	$136.95	$136.90
Purchase #2	$213.34	8.637%	$231.7662	$231.77	$231.75	$231.80
Purchase #3	$53.79	11.780%	$60.1265	$60.13	$60.15	$60.10
Purchase #4	$176.89	4.778%	$185.3418	$185.34	$185.35	$185.30
Purchase #5	$194.68	3.205%	$200.9195	$200.92	$200.90	$200.90
Purchase #6	$84.49	7.625%	$90.9324	$90.93	$90.95	$90.90
Purchase #7	$136.68	10.790%	$151.4278	$151.43	$151.45	$151.40
7 purchase totals =	$984.84		$1,057.4576	$1,057.46	$1,057.50	$1,057.30