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	$141.85	9.566%	$155.4194	$155.42	$155.40	$155.40
Purchase #2	$246.71	13.700%	$280.5093	$280.51	$280.50	$280.50
Purchase #3	$139.76	11.732%	$156.1566	$156.16	$156.15	$156.20
Purchase #4	$146.46	10.855%	$162.3582	$162.36	$162.35	$162.40
Purchase #5	$32.77	13.511%	$37.1976	$37.20	$37.20	$37.20
Purchase #6	$181.44	6.727%	$193.6455	$193.65	$193.65	$193.60
Purchase #7	$104.84	6.472%	$111.6252	$111.63	$111.65	$111.60
7 purchase totals =	$993.83		$1,096.9118	$1,096.93	$1,096.90	$1,096.90