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	$243.56	11.181%	$270.7924	$270.79	$270.80	$270.80
Purchase #2	$68.77	5.821%	$72.7731	$72.77	$72.75	$72.80
Purchase #3	$184.36	12.307%	$207.0492	$207.05	$207.05	$207.00
Purchase #4	$37.43	4.726%	$39.1989	$39.20	$39.20	$39.20
Purchase #5	$181.92	13.564%	$206.5956	$206.60	$206.60	$206.60
Purchase #6	$196.32	13.292%	$222.4149	$222.41	$222.40	$222.40
Purchase #7	$96.38	3.629%	$99.8776	$99.88	$99.90	$99.90
7 purchase totals =	$1,008.74		$1,118.7017	$1,118.70	$1,118.70	$1,118.70