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	$89.63	11.635%	$100.0585	$100.06	$100.05	$100.10
Purchase #2	$243.58	5.686%	$257.43	$257.43	$257.45	$257.40
Purchase #3	$238.62	4.300%	$248.8807	$248.88	$248.90	$248.90
Purchase #4	$133.77	6.234%	$142.1092	$142.11	$142.10	$142.10
Purchase #5	$83.96	3.117%	$86.577	$86.58	$86.60	$86.60
Purchase #6	$213.35	6.671%	$227.5826	$227.58	$227.60	$227.60
Purchase #7	$108.47	7.753%	$116.8797	$116.88	$116.90	$116.90
7 purchase totals =	$1,111.38		$1,179.5177	$1,179.52	$1,179.60	$1,179.60