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	$143.72	12.285%	$161.376	$161.38	$161.40	$161.40
Purchase #2	$148.32	9.155%	$161.8987	$161.90	$161.90	$161.90
Purchase #3	$49.76	9.619%	$54.5464	$54.55	$54.55	$54.50
Purchase #4	$133.34	10.541%	$147.3954	$147.40	$147.40	$147.40
Purchase #5	$36.80	4.611%	$38.4968	$38.50	$38.50	$38.50
Purchase #6	$37.93	5.708%	$40.095	$40.10	$40.10	$40.10
Purchase #7	$176.69	6.137%	$187.5335	$187.53	$187.55	$187.50
7 purchase totals =	$726.56		$791.3418	$791.36	$791.40	$791.30