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	$75.72	4.314%	$78.9866	$78.99	$79.00	$79.00
Purchase #2	$241.78	9.840%	$265.5712	$265.57	$265.55	$265.60
Purchase #3	$232.35	3.614%	$240.7471	$240.75	$240.75	$240.70
Purchase #4	$99.32	4.630%	$103.9185	$103.92	$103.90	$103.90
Purchase #5	$75.95	9.366%	$83.0635	$83.06	$83.05	$83.10
Purchase #6	$198.59	10.456%	$219.3546	$219.35	$219.35	$219.40
Purchase #7	$114.58	4.673%	$119.9343	$119.93	$119.95	$119.90
7 purchase totals =	$1,038.29		$1,111.5758	$1,111.57	$1,111.55	$1,111.60