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	$108.87	13.399%	$123.4575	$123.46	$123.45	$123.50
Purchase #2	$46.81	8.767%	$50.9138	$50.91	$50.90	$50.90
Purchase #3	$111.36	7.706%	$119.9414	$119.94	$119.95	$119.90
Purchase #4	$224.66	13.736%	$255.5193	$255.52	$255.50	$255.50
Purchase #5	$131.67	9.820%	$144.6	$144.60	$144.60	$144.60
Purchase #6	$211.33	13.727%	$240.3393	$240.34	$240.35	$240.30
Purchase #7	$169.86	9.858%	$186.6048	$186.60	$186.60	$186.60
7 purchase totals =	$1,004.56		$1,121.3761	$1,121.37	$1,121.35	$1,121.30