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	$172.53	12.207%	$193.5907	$193.59	$193.60	$193.60
Purchase #2	$228.87	9.578%	$250.7912	$250.79	$250.80	$250.80
Purchase #3	$78.91	10.512%	$87.205	$87.21	$87.20	$87.20
Purchase #4	$118.85	4.259%	$123.9118	$123.91	$123.90	$123.90
Purchase #5	$131.81	12.867%	$148.77	$148.77	$148.75	$148.80
Purchase #6	$40.91	9.619%	$44.8451	$44.85	$44.85	$44.80
Purchase #7	$68.95	5.614%	$72.8209	$72.82	$72.80	$72.80
7 purchase totals =	$840.83		$921.9347	$921.94	$921.90	$921.90