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	$121.44	12.587%	$136.7257	$136.73	$136.75	$136.70
Purchase #2	$142.34	7.860%	$153.5279	$153.53	$153.55	$153.50
Purchase #3	$112.53	13.210%	$127.3952	$127.40	$127.40	$127.40
Purchase #4	$76.31	12.150%	$85.5817	$85.58	$85.60	$85.60
Purchase #5	$31.68	6.445%	$33.7218	$33.72	$33.70	$33.70
Purchase #6	$245.59	11.458%	$273.7297	$273.73	$273.75	$273.70
Purchase #7	$50.64	6.586%	$53.9752	$53.98	$54.00	$54.00
7 purchase totals =	$780.53		$864.6572	$864.67	$864.75	$864.60