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	$126.78	12.606%	$142.7619	$142.76	$142.75	$142.80
Purchase #2	$250.42	12.693%	$282.2058	$282.21	$282.20	$282.20
Purchase #3	$182.63	3.342%	$188.7335	$188.73	$188.75	$188.70
Purchase #4	$131.89	6.512%	$140.4787	$140.48	$140.50	$140.50
Purchase #5	$230.73	13.661%	$262.25	$262.25	$262.25	$262.30
Purchase #6	$104.87	9.512%	$114.8452	$114.85	$114.85	$114.80
Purchase #7	$200.93	10.145%	$221.3143	$221.31	$221.30	$221.30
7 purchase totals =	$1,228.25		$1,352.5894	$1,352.59	$1,352.60	$1,352.60