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	$75.80	3.656%	$78.5712	$78.57	$78.55	$78.60
Purchase #2	$142.66	12.761%	$160.8648	$160.86	$160.85	$160.90
Purchase #3	$25.91	7.642%	$27.89	$27.89	$27.90	$27.90
Purchase #4	$171.90	13.823%	$195.6617	$195.66	$195.65	$195.70
Purchase #5	$67.80	10.131%	$74.6688	$74.67	$74.65	$74.70
Purchase #6	$119.93	6.542%	$127.7758	$127.78	$127.80	$127.80
Purchase #7	$69.25	13.494%	$78.5946	$78.59	$78.60	$78.60
7 purchase totals =	$673.25		$744.0269	$744.02	$744.00	$744.20