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	$85.63	4.869%	$89.7993	$89.80	$89.80	$89.80
Purchase #2	$34.37	12.796%	$38.768	$38.77	$38.75	$38.80
Purchase #3	$80.64	9.190%	$88.0508	$88.05	$88.05	$88.10
Purchase #4	$247.59	12.342%	$278.1476	$278.15	$278.15	$278.10
Purchase #5	$198.74	11.151%	$220.9015	$220.90	$220.90	$220.90
Purchase #6	$166.52	10.254%	$183.595	$183.60	$183.60	$183.60
Purchase #7	$136.96	9.850%	$150.4506	$150.45	$150.45	$150.50
7 purchase totals =	$950.45		$1,049.7128	$1,049.72	$1,049.70	$1,049.80