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	$66.88	6.854%	$71.464	$71.46	$71.45	$71.50
Purchase #2	$153.25	9.186%	$167.3275	$167.33	$167.35	$167.30
Purchase #3	$54.86	8.418%	$59.4781	$59.48	$59.50	$59.50
Purchase #4	$235.98	7.499%	$253.6761	$253.68	$253.70	$253.70
Purchase #5	$91.39	7.632%	$98.3649	$98.36	$98.35	$98.40
Purchase #6	$222.62	12.177%	$249.7284	$249.73	$249.75	$249.70
Purchase #7	$219.64	5.408%	$231.5181	$231.52	$231.50	$231.50
7 purchase totals =	$1,044.62		$1,131.5571	$1,131.56	$1,131.60	$1,131.60