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	$143.26	12.156%	$160.6747	$160.67	$160.65	$160.70
Purchase #2	$209.63	6.611%	$223.4886	$223.49	$223.50	$223.50
Purchase #3	$50.53	12.273%	$56.7315	$56.73	$56.75	$56.70
Purchase #4	$209.42	10.632%	$231.6855	$231.69	$231.70	$231.70
Purchase #5	$75.31	9.520%	$82.4795	$82.48	$82.50	$82.50
Purchase #6	$70.59	11.662%	$78.8222	$78.82	$78.80	$78.80
Purchase #7	$121.69	4.293%	$126.9142	$126.91	$126.90	$126.90
7 purchase totals =	$880.43		$960.7962	$960.79	$960.80	$960.80