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	$232.83	11.163%	$258.8208	$258.82	$258.80	$258.80
Purchase #2	$19.61	7.156%	$21.0133	$21.01	$21.00	$21.00
Purchase #3	$232.86	13.365%	$263.9817	$263.98	$264.00	$264.00
Purchase #4	$159.26	10.768%	$176.4091	$176.41	$176.40	$176.40
Purchase #5	$190.38	6.547%	$202.8442	$202.84	$202.85	$202.80
Purchase #6	$81.36	10.441%	$89.8548	$89.85	$89.85	$89.90
Purchase #7	$119.39	3.290%	$123.3179	$123.32	$123.30	$123.30
7 purchase totals =	$1,035.69		$1,136.2418	$1,136.23	$1,136.20	$1,136.20