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	$243.50	5.426%	$256.7123	$256.71	$256.70	$256.70
Purchase #2	$167.57	3.604%	$173.6092	$173.61	$173.60	$173.60
Purchase #3	$171.40	8.874%	$186.61	$186.61	$186.60	$186.60
Purchase #4	$34.55	12.618%	$38.9095	$38.91	$38.90	$38.90
Purchase #5	$196.45	10.405%	$216.8906	$216.89	$216.90	$216.90
Purchase #6	$127.33	10.309%	$140.4564	$140.46	$140.45	$140.50
Purchase #7	$175.26	8.807%	$190.6951	$190.70	$190.70	$190.70
7 purchase totals =	$1,116.06		$1,203.8831	$1,203.89	$1,203.85	$1,203.90