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	$60.63	10.480%	$66.984	$66.98	$67.00	$67.00
Purchase #2	$156.25	8.456%	$169.4625	$169.46	$169.45	$169.50
Purchase #3	$37.94	6.410%	$40.372	$40.37	$40.35	$40.40
Purchase #4	$38.89	3.352%	$40.1936	$40.19	$40.20	$40.20
Purchase #5	$6.58	11.122%	$7.3118	$7.31	$7.30	$7.30
Purchase #6	$206.51	5.241%	$217.3332	$217.33	$217.35	$217.30
Purchase #7	$182.75	3.227%	$188.6473	$188.65	$188.65	$188.60
7 purchase totals =	$689.55		$730.3044	$730.29	$730.30	$730.30