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	$169.60	7.366%	$182.0927	$182.09	$182.10	$182.10
Purchase #2	$156.53	9.590%	$171.5412	$171.54	$171.55	$171.50
Purchase #3	$142.67	12.684%	$160.7663	$160.77	$160.75	$160.80
Purchase #4	$165.43	9.618%	$181.3411	$181.34	$181.35	$181.30
Purchase #5	$13.74	13.151%	$15.5469	$15.55	$15.55	$15.50
Purchase #6	$172.64	6.230%	$183.3955	$183.40	$183.40	$183.40
Purchase #7	$80.38	4.352%	$83.8781	$83.88	$83.90	$83.90
7 purchase totals =	$900.99		$978.5618	$978.57	$978.60	$978.50