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	$79.51	12.638%	$89.5585	$89.56	$89.55	$89.60
Purchase #2	$247.50	13.219%	$280.217	$280.22	$280.20	$280.20
Purchase #3	$140.97	4.284%	$147.0092	$147.01	$147.00	$147.00
Purchase #4	$93.73	10.240%	$103.328	$103.33	$103.35	$103.30
Purchase #5	$207.78	5.437%	$219.077	$219.08	$219.10	$219.10
Purchase #6	$71.46	5.472%	$75.3703	$75.37	$75.35	$75.40
Purchase #7	$71.87	12.403%	$80.784	$80.78	$80.80	$80.80
7 purchase totals =	$912.82		$995.3440	$995.35	$995.35	$995.40