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	$104.28	9.234%	$113.9092	$113.91	$113.90	$113.90
Purchase #2	$226.76	6.669%	$241.8826	$241.88	$241.90	$241.90
Purchase #3	$41.91	6.238%	$44.5243	$44.52	$44.50	$44.50
Purchase #4	$185.96	5.445%	$196.0855	$196.09	$196.10	$196.10
Purchase #5	$102.50	12.639%	$115.455	$115.46	$115.45	$115.50
Purchase #6	$91.28	10.773%	$101.1136	$101.11	$101.10	$101.10
Purchase #7	$96.80	3.128%	$99.8279	$99.83	$99.85	$99.80
7 purchase totals =	$849.49		$912.7981	$912.80	$912.80	$912.80