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	$71.47	10.421%	$78.9179	$78.92	$78.90	$78.90
Purchase #2	$162.77	9.774%	$178.6791	$178.68	$178.70	$178.70
Purchase #3	$236.81	13.516%	$268.8172	$268.82	$268.80	$268.80
Purchase #4	$103.60	5.697%	$109.5021	$109.50	$109.50	$109.50
Purchase #5	$180.34	8.510%	$195.6869	$195.69	$195.70	$195.70
Purchase #6	$229.70	11.342%	$255.7526	$255.75	$255.75	$255.80
Purchase #7	$210.82	5.547%	$222.5142	$222.51	$222.50	$222.50
7 purchase totals =	$1,195.51		$1,309.8700	$1,309.87	$1,309.85	$1,309.90