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	$89.59	10.753%	$99.2236	$99.22	$99.20	$99.20
Purchase #2	$131.85	9.169%	$143.9393	$143.94	$143.95	$143.90
Purchase #3	$195.44	13.701%	$222.2172	$222.22	$222.20	$222.20
Purchase #4	$108.28	12.648%	$121.9753	$121.98	$122.00	$122.00
Purchase #5	$73.50	11.860%	$82.2171	$82.22	$82.20	$82.20
Purchase #6	$76.37	13.356%	$86.57	$86.57	$86.55	$86.60
Purchase #7	$241.46	12.781%	$272.321	$272.32	$272.30	$272.30
7 purchase totals =	$916.49		$1,028.4635	$1,028.47	$1,028.40	$1,028.40