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	$100.50	12.818%	$113.3821	$113.38	$113.40	$113.40
Purchase #2	$96.48	3.359%	$99.7208	$99.72	$99.70	$99.70
Purchase #3	$213.55	10.712%	$236.4255	$236.43	$236.45	$236.40
Purchase #4	$99.51	8.419%	$107.8877	$107.89	$107.90	$107.90
Purchase #5	$167.69	10.103%	$184.6317	$184.63	$184.65	$184.60
Purchase #6	$136.88	12.278%	$153.6861	$153.69	$153.70	$153.70
Purchase #7	$211.82	4.622%	$221.6103	$221.61	$221.60	$221.60
7 purchase totals =	$1,026.43		$1,117.3442	$1,117.35	$1,117.40	$1,117.30