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	$243.38	8.647%	$264.4251	$264.43	$264.45	$264.40
Purchase #2	$195.94	13.261%	$221.9236	$221.92	$221.90	$221.90
Purchase #3	$130.85	4.455%	$136.6794	$136.68	$136.70	$136.70
Purchase #4	$125.53	13.303%	$142.2293	$142.23	$142.25	$142.20
Purchase #5	$129.52	12.652%	$145.9069	$145.91	$145.90	$145.90
Purchase #6	$180.86	9.725%	$198.4486	$198.45	$198.45	$198.40
Purchase #7	$176.77	13.281%	$200.2468	$200.25	$200.25	$200.20
7 purchase totals =	$1,182.85		$1,309.8597	$1,309.87	$1,309.90	$1,309.70