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	$214.68	13.268%	$243.1637	$243.16	$243.15	$243.20
Purchase #2	$53.54	7.516%	$57.5641	$57.56	$57.55	$57.60
Purchase #3	$175.90	12.266%	$197.4759	$197.48	$197.50	$197.50
Purchase #4	$50.59	6.254%	$53.7539	$53.75	$53.75	$53.80
Purchase #5	$105.37	5.574%	$111.2433	$111.24	$111.25	$111.20
Purchase #6	$44.55	3.544%	$46.1289	$46.13	$46.15	$46.10
Purchase #7	$146.78	3.110%	$151.3449	$151.34	$151.35	$151.30
7 purchase totals =	$791.41		$860.6747	$860.66	$860.70	$860.70