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	$25.61	9.547%	$28.055	$28.06	$28.05	$28.10
Purchase #2	$140.75	13.862%	$160.2608	$160.26	$160.25	$160.30
Purchase #3	$38.71	8.812%	$42.1211	$42.12	$42.10	$42.10
Purchase #4	$224.52	5.314%	$236.451	$236.45	$236.45	$236.50
Purchase #5	$72.46	13.796%	$82.4566	$82.46	$82.45	$82.50
Purchase #6	$225.53	6.135%	$239.3663	$239.37	$239.35	$239.40
Purchase #7	$238.80	4.742%	$250.1239	$250.12	$250.10	$250.10
7 purchase totals =	$966.38		$1,038.8347	$1,038.84	$1,038.75	$1,039.00